feat(v1.8.0): IMPL_06 Post-Update Changelog Dialog

- Add UpdateChangelogSheet.kt with Material 3 ModalBottomSheet
- Show changelog automatically on first launch after update
- Load changelog from F-Droid metadata via assets (single source of truth)
- Add copyChangelogsToAssets Gradle task (runs before preBuild)
- Copy F-Droid changelogs to /assets/changelogs/{locale}/ at build time
- Store last shown version in SharedPreferences (last_shown_changelog_version)
- Add ClickableText for GitHub CHANGELOG.md link (opens in browser)
- Add update_changelog_title and update_changelog_dismiss strings (EN + DE)
- Add KEY_LAST_SHOWN_CHANGELOG_VERSION constant
- Integrate UpdateChangelogSheet in ComposeMainActivity
- Add Test Mode in Debug Settings with "Reset Changelog Dialog" button
- Add SettingsViewModel.resetChangelogVersion() for testing
- Add test mode strings (debug_test_section, debug_reset_changelog, etc.)
- Update F-Droid changelogs (20.txt) with focus on key features
- Add exception logging in loadChangelog() function
- Add /app/src/main/assets/changelogs/ to .gitignore
- Dialog dismissable via button or swipe gesture
- One-time display per versionCode

Adds post-update changelog dialog with automatic F-Droid changelog reuse.
F-Droid changelogs are the single source of truth for both F-Droid metadata
and in-app display. Gradle task copies changelogs to assets at build time.
Users see localized changelog (DE/EN) based on app language.

android/.gitignore

@@ -18,3 +18,4 @@ local.properties
 key.properties
 *.jks
 *.keystore
+/app/src/main/assets/changelogs/

android/app/build.gradle.kts

@@ -199,4 +199,34 @@ detekt {
     
     // Parallel-Verarbeitung für schnellere Checks
     parallel = true
+}
+
+// 📋 v1.8.0: Copy F-Droid changelogs to assets for post-update dialog
+// Single source of truth: F-Droid changelogs are reused in the app
+tasks.register<Copy>("copyChangelogsToAssets") {
+    description = "Copies F-Droid changelogs to app assets for post-update dialog"
+    
+    from("$rootDir/../fastlane/metadata/android") {
+        include("*/changelogs/*.txt")
+    }
+    
+    into("$projectDir/src/main/assets/changelogs")
+    
+    // Preserve directory structure: en-US/20.txt, de-DE/20.txt
+    eachFile {
+        val parts = relativePath.segments
+        if (parts.size >= 3) {
+            // parts[0] = locale (en-US, de-DE)
+            // parts[1] = "changelogs"
+            // parts[2] = version file (20.txt)
+            relativePath = RelativePath(true, parts[0], parts[2])
+        }
+    }
+    
+    includeEmptyDirs = false
+}
+
+// Run before preBuild to ensure changelogs are available
+tasks.named("preBuild") {
+    dependsOn("copyChangelogsToAssets")
 }

android/app/src/main/java/dev/dettmer/simplenotes/ui/main/ComposeMainActivity.kt

@@ -170,6 +170,9 @@ class ComposeMainActivity : ComponentActivity() {
                     onOpenSettings = { openSettings() },
                     onCreateNote = { noteType -> createNote(noteType) }
                 )
+                
+                // v1.8.0: Post-Update Changelog (shows once after update)
+                UpdateChangelogSheet()
             }
         }
     }

android/app/src/main/java/dev/dettmer/simplenotes/ui/main/UpdateChangelogSheet.kt

@@ -0,0 +1,211 @@
+package dev.dettmer.simplenotes.ui.main
+
+import android.content.Context
+import android.content.Intent
+import android.net.Uri
+import androidx.appcompat.app.AppCompatDelegate
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.Spacer
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.layout.height
+import androidx.compose.foundation.layout.navigationBarsPadding
+import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.text.ClickableText
+import androidx.compose.material3.Button
+import androidx.compose.material3.ExperimentalMaterial3Api
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.ModalBottomSheet
+import androidx.compose.material3.Text
+import androidx.compose.material3.rememberModalBottomSheetState
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.rememberCoroutineScope
+import androidx.compose.runtime.setValue
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.platform.LocalContext
+import androidx.compose.ui.res.stringResource
+import androidx.compose.ui.text.SpanStyle
+import androidx.compose.ui.text.buildAnnotatedString
+import androidx.compose.ui.text.font.FontWeight
+import androidx.compose.ui.text.style.TextDecoration
+import androidx.compose.ui.text.withStyle
+import androidx.compose.ui.unit.dp
+import dev.dettmer.simplenotes.BuildConfig
+import dev.dettmer.simplenotes.R
+import dev.dettmer.simplenotes.utils.Constants
+import dev.dettmer.simplenotes.utils.Logger
+import kotlinx.coroutines.launch
+
+/**
+ * v1.8.0: Post-Update Changelog Bottom Sheet
+ * 
+ * Shows a subtle changelog on first launch after an update.
+ * - Reads changelog from raw resources (supports DE/EN)
+ * - Only shows once per versionCode (stored in SharedPreferences)
+ * - Uses Material 3 ModalBottomSheet with built-in slide-up animation
+ * - Dismissable via button or swipe-down
+ */
+@OptIn(ExperimentalMaterial3Api::class)
+@Composable
+fun UpdateChangelogSheet() {
+    val context = LocalContext.current
+    val prefs = remember {
+        context.getSharedPreferences(Constants.PREFS_NAME, Context.MODE_PRIVATE)
+    }
+    
+    val currentVersionCode = BuildConfig.VERSION_CODE
+    val lastShownVersion = prefs.getInt(Constants.KEY_LAST_SHOWN_CHANGELOG_VERSION, 0)
+    
+    // Only show if this is a new version
+    var showSheet by remember { mutableStateOf(currentVersionCode > lastShownVersion) }
+    
+    if (!showSheet) return
+    
+    val sheetState = rememberModalBottomSheetState(skipPartiallyExpanded = true)
+    val scope = rememberCoroutineScope()
+    
+    // Load changelog text based on current locale
+    val changelogText = remember {
+        loadChangelog(context)
+    }
+    
+    ModalBottomSheet(
+        onDismissRequest = {
+            showSheet = false
+            prefs.edit()
+                .putInt(Constants.KEY_LAST_SHOWN_CHANGELOG_VERSION, currentVersionCode)
+                .apply()
+        },
+        sheetState = sheetState,
+        containerColor = MaterialTheme.colorScheme.surface,
+        contentColor = MaterialTheme.colorScheme.onSurface,
+        tonalElevation = 2.dp
+    ) {
+        Column(
+            modifier = Modifier
+                .fillMaxWidth()
+                .padding(horizontal = 24.dp)
+                .navigationBarsPadding(),
+            horizontalAlignment = Alignment.CenterHorizontally
+        ) {
+            // Title
+            Text(
+                text = stringResource(R.string.update_changelog_title),
+                style = MaterialTheme.typography.headlineSmall,
+                fontWeight = FontWeight.SemiBold,
+                color = MaterialTheme.colorScheme.primary
+            )
+            
+            Spacer(modifier = Modifier.height(16.dp))
+            
+            // Changelog content with clickable links
+            val annotatedText = buildAnnotatedString {
+                val lines = changelogText.split("\n")
+                lines.forEachIndexed { index, line ->
+                    if (line.startsWith("http://") || line.startsWith("https://")) {
+                        // Make URLs clickable
+                        pushStringAnnotation(
+                            tag = "URL",
+                            annotation = line.trim()
+                        )
+                        withStyle(
+                            style = SpanStyle(
+                                color = MaterialTheme.colorScheme.primary,
+                                textDecoration = TextDecoration.Underline
+                            )
+                        ) {
+                            append(line)
+                        }
+                        pop()
+                    } else {
+                        append(line)
+                    }
+                    if (index < lines.size - 1) append("\n")
+                }
+            }
+            
+            ClickableText(
+                text = annotatedText,
+                style = MaterialTheme.typography.bodyMedium.copy(
+                    color = MaterialTheme.colorScheme.onSurfaceVariant
+                ),
+                modifier = Modifier.fillMaxWidth(),
+                onClick = { offset ->
+                    annotatedText.getStringAnnotations(tag = "URL", start = offset, end = offset)
+                        .firstOrNull()?.let { annotation ->
+                            val intent = Intent(Intent.ACTION_VIEW, Uri.parse(annotation.item))
+                            context.startActivity(intent)
+                        }
+                }
+            )
+            
+            Spacer(modifier = Modifier.height(24.dp))
+            
+            // Dismiss button
+            Button(
+                onClick = {
+                    scope.launch {
+                        sheetState.hide()
+                    }.invokeOnCompletion {
+                        showSheet = false
+                        prefs.edit()
+                            .putInt(Constants.KEY_LAST_SHOWN_CHANGELOG_VERSION, currentVersionCode)
+                            .apply()
+                    }
+                },
+                modifier = Modifier
+                    .fillMaxWidth()
+                    .padding(horizontal = 32.dp)
+            ) {
+                Text(stringResource(R.string.update_changelog_dismiss))
+            }
+            
+            Spacer(modifier = Modifier.height(16.dp))
+        }
+    }
+}
+
+/**
+ * Load changelog text from assets based on current app locale and versionCode.
+ * Changelogs are copied from /fastlane/metadata/android/{locale}/changelogs/{versionCode}.txt
+ * at build time, providing a single source of truth for F-Droid and in-app display.
+ * Falls back to English if the localized version is not available.
+ */
+private fun loadChangelog(context: Context): String {
+    val currentLocale = AppCompatDelegate.getApplicationLocales()
+    val languageCode = if (currentLocale.isEmpty) {
+        // System default — check system locale
+        java.util.Locale.getDefault().language
+    } else {
+        currentLocale.get(0)?.language ?: "en"
+    }
+    
+    // Map language code to F-Droid locale directory
+    val localeDir = when (languageCode) {
+        "de" -> "de-DE"
+        else -> "en-US"
+    }
+    
+    val versionCode = BuildConfig.VERSION_CODE
+    val changelogPath = "changelogs/$localeDir/$versionCode.txt"
+    
+    return try {
+        context.assets.open(changelogPath)
+            .bufferedReader()
+            .use { it.readText() }
+    } catch (e: Exception) {
+        Logger.e("UpdateChangelogSheet", "Failed to load changelog for locale: $localeDir", e)
+        // Fallback to English
+        try {
+            context.assets.open("changelogs/en-US/$versionCode.txt")
+                .bufferedReader()
+                .use { it.readText() }
+        } catch (e2: Exception) {
+            Logger.e("UpdateChangelogSheet", "Failed to load English fallback changelog", e2)
+            "v${BuildConfig.VERSION_NAME}"
+        }
+    }
+}

android/app/src/main/java/dev/dettmer/simplenotes/ui/settings/SettingsViewModel.kt

@@ -811,6 +811,16 @@ class SettingsViewModel(application: Application) : AndroidViewModel(application
     
     fun getLogFile() = Logger.getLogFile(getApplication())
     
+    /**
+     * v1.8.0: Reset changelog version to force showing the changelog dialog on next start
+     * Used for testing the post-update changelog feature
+     */
+    fun resetChangelogVersion() {
+        prefs.edit()
+            .putInt(Constants.KEY_LAST_SHOWN_CHANGELOG_VERSION, 0)
+            .apply()
+    }
+    
     // ═══════════════════════════════════════════════════════════════════════
     // Helper
     // ═══════════════════════════════════════════════════════════════════════

android/app/src/main/java/dev/dettmer/simplenotes/ui/settings/screens/DebugSettingsScreen.kt

@@ -119,6 +119,31 @@ fun DebugSettingsScreen(
             )
             
             Spacer(modifier = Modifier.height(16.dp))
+            
+            SettingsDivider()
+            
+            // v1.8.0: Test Mode Section
+            SettingsSectionHeader(text = stringResource(R.string.debug_test_section))
+            
+            Spacer(modifier = Modifier.height(8.dp))
+            
+            // Info about test mode
+            SettingsInfoCard(
+                text = stringResource(R.string.debug_reset_changelog_desc)
+            )
+            
+            val changelogResetToast = stringResource(R.string.debug_changelog_reset)
+            
+            SettingsButton(
+                text = stringResource(R.string.debug_reset_changelog),
+                onClick = {
+                    viewModel.resetChangelogVersion()
+                    android.widget.Toast.makeText(context, changelogResetToast, android.widget.Toast.LENGTH_SHORT).show()
+                },
+                modifier = Modifier.padding(horizontal = 16.dp)
+            )
+
+            Spacer(modifier = Modifier.height(16.dp))
         }
     }
     

android/app/src/main/java/dev/dettmer/simplenotes/utils/Constants.kt

@@ -79,4 +79,7 @@ object Constants {
     const val KEY_SORT_DIRECTION = "sort_direction"
     const val DEFAULT_SORT_OPTION = "updatedAt"
     const val DEFAULT_SORT_DIRECTION = "desc"
+    
+    // 📋 v1.8.0: Post-Update Changelog
+    const val KEY_LAST_SHOWN_CHANGELOG_VERSION = "last_shown_changelog_version"
 }

android/app/src/main/res/values-de/strings.xml

@@ -403,6 +403,10 @@
     <string name="debug_delete_logs">🗑️ Logs löschen</string>
     <string name="debug_delete_logs_title">Logs löschen?</string>
     <string name="debug_delete_logs_message">Alle gespeicherten Sync-Logs werden unwiderruflich gelöscht.</string>
+    <string name="debug_test_section">Test-Modus</string>
+    <string name="debug_reset_changelog">Changelog-Dialog zurücksetzen</string>
+    <string name="debug_reset_changelog_desc">Changelog beim nächsten App-Start anzeigen</string>
+    <string name="debug_changelog_reset">Changelog wird beim nächsten Start angezeigt</string>
     <!-- Legacy -->
     <string name="file_logging_privacy_notice">ℹ️ Datenschutz: Logs werden nur lokal auf deinem Gerät gespeichert und niemals an externe Server gesendet. Die Logs enthalten Sync-Aktivitäten zur Fehlerdiagnose. Du kannst sie jederzeit löschen oder exportieren.</string>
     
@@ -443,6 +447,10 @@
     <string name="about_changelog_title">Changelog</string>
     <string name="about_changelog_subtitle">Vollständige Versionshistorie</string>
     
+    <!-- v1.8.0: Post-Update Changelog Dialog -->
+    <string name="update_changelog_title">Was ist neu</string>
+    <string name="update_changelog_dismiss">Alles klar!</string>
+    
     <!-- v1.8.0: Backup Progress -->
     <string name="backup_progress_creating">Backup wird erstellt…</string>
     <string name="backup_progress_restoring">Backup wird wiederhergestellt…</string>

android/app/src/main/res/values/strings.xml

@@ -403,6 +403,10 @@
     <string name="debug_delete_logs">🗑️ Delete Logs</string>
     <string name="debug_delete_logs_title">Delete logs?</string>
     <string name="debug_delete_logs_message">All saved sync logs will be permanently deleted.</string>
+    <string name="debug_test_section">Test Mode</string>
+    <string name="debug_reset_changelog">Reset Changelog Dialog</string>
+    <string name="debug_reset_changelog_desc">Show changelog on next app start</string>
+    <string name="debug_changelog_reset">Changelog will show on next start</string>
     <!-- Legacy -->
     <string name="file_logging_privacy_notice">ℹ️ Privacy: Logs are only stored locally on your device and are never sent to external servers. Logs contain sync activities for troubleshooting. You can delete or export them at any time.</string>
     
@@ -443,6 +447,10 @@
     <string name="about_changelog_title">Changelog</string>
     <string name="about_changelog_subtitle">Full version history</string>
     
+    <!-- v1.8.0: Post-Update Changelog Dialog -->
+    <string name="update_changelog_title">What\'s New</string>
+    <string name="update_changelog_dismiss">Got it!</string>
+    
     <!-- v1.8.0: Backup Progress -->
     <string name="backup_progress_creating">Creating backup…</string>
     <string name="backup_progress_restoring">Restoring backup…</string>