feat(v1.8.0): IMPL_021 Sync Status Legend

- New SyncStatusLegendDialog.kt showing all 5 sync status icons with descriptions
- Help button (?) in MainScreen TopAppBar (only visible when sync available)
- Localized strings (English + German) for all 5 status explanations
- Material You design with consistent colors matching NoteCard icons
- Dialog shows: Synced, Pending, Conflict, Local only, Deleted on server

IMPL_021_SYNC_STATUS_LEGEND.md

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

@@ -17,6 +17,7 @@ import androidx.compose.material.icons.filled.Delete
 import androidx.compose.material.icons.filled.Refresh
 import androidx.compose.material.icons.filled.SelectAll
 import androidx.compose.material.icons.filled.Settings
+import androidx.compose.material.icons.automirrored.outlined.HelpOutline
 import androidx.compose.material3.ExperimentalMaterial3Api
 // FabPosition nicht mehr benötigt - FAB wird manuell platziert
 import androidx.compose.material3.Icon
@@ -53,6 +54,7 @@ import dev.dettmer.simplenotes.ui.main.components.NoteTypeFAB
 import dev.dettmer.simplenotes.ui.main.components.NotesList
 import dev.dettmer.simplenotes.ui.main.components.NotesStaggeredGrid
 import dev.dettmer.simplenotes.ui.main.components.SyncStatusBanner
+import dev.dettmer.simplenotes.ui.main.components.SyncStatusLegendDialog
 import kotlinx.coroutines.launch
 
 private const val TIMESTAMP_UPDATE_INTERVAL_MS = 30_000L
@@ -92,6 +94,9 @@ fun MainScreen(
     // Delete confirmation dialog state
     var showBatchDeleteDialog by remember { mutableStateOf(false) }
     
+    // 🆕 v1.8.0: Sync status legend dialog
+    var showSyncLegend by remember { mutableStateOf(false) }
+    
     val snackbarHostState = remember { SnackbarHostState() }
     val scope = rememberCoroutineScope()
     val listState = rememberLazyListState()
@@ -170,6 +175,8 @@ fun MainScreen(
             ) {
                 MainTopBar(
                     syncEnabled = canSync,
+                    showSyncLegend = isSyncAvailable,  // 🆕 v1.8.0: Nur wenn Sync verfügbar
+                    onSyncLegendClick = { showSyncLegend = true },  // 🆕 v1.8.0
                     onSyncClick = { viewModel.triggerManualSync("toolbar") },
                     onSettingsClick = onOpenSettings
                 )
@@ -276,6 +283,13 @@ fun MainScreen(
                 }
             )
         }
+        
+        // 🆕 v1.8.0: Sync Status Legend Dialog
+        if (showSyncLegend) {
+            SyncStatusLegendDialog(
+                onDismiss = { showSyncLegend = false }
+            )
+        }
     }
 }
 
@@ -283,6 +297,8 @@ fun MainScreen(
 @Composable
 private fun MainTopBar(
     syncEnabled: Boolean,
+    showSyncLegend: Boolean,  // 🆕 v1.8.0: Ob der Hilfe-Button sichtbar sein soll
+    onSyncLegendClick: () -> Unit,  // 🆕 v1.8.0
     onSyncClick: () -> Unit,
     onSettingsClick: () -> Unit
 ) {
@@ -294,6 +310,15 @@ private fun MainTopBar(
             )
         },
         actions = {
+            // 🆕 v1.8.0: Sync Status Legend Button (nur wenn Sync verfügbar)
+            if (showSyncLegend) {
+                IconButton(onClick = onSyncLegendClick) {
+                    Icon(
+                        imageVector = Icons.AutoMirrored.Outlined.HelpOutline,
+                        contentDescription = stringResource(R.string.sync_legend_button)
+                    )
+                }
+            }
             IconButton(
                 onClick = onSyncClick,
                 enabled = syncEnabled

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

@@ -0,0 +1,148 @@
+package dev.dettmer.simplenotes.ui.main.components
+
+import androidx.compose.foundation.layout.Arrangement
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.Row
+import androidx.compose.foundation.layout.Spacer
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.layout.size
+import androidx.compose.foundation.layout.width
+import androidx.compose.material.icons.Icons
+import androidx.compose.material.icons.filled.Warning
+import androidx.compose.material.icons.outlined.CloudDone
+import androidx.compose.material.icons.outlined.CloudOff
+import androidx.compose.material.icons.outlined.CloudSync
+import androidx.compose.material3.AlertDialog
+import androidx.compose.material3.HorizontalDivider
+import androidx.compose.material3.Icon
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.Text
+import androidx.compose.material3.TextButton
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.graphics.vector.ImageVector
+import androidx.compose.ui.res.stringResource
+import androidx.compose.ui.unit.dp
+import dev.dettmer.simplenotes.R
+
+/**
+ * 🆕 v1.8.0: Dialog showing the sync status icon legend
+ * 
+ * Displays all 5 SyncStatus values with their icons, colors, 
+ * and descriptions. Helps users understand what each icon means.
+ */
+@Composable
+fun SyncStatusLegendDialog(
+    onDismiss: () -> Unit
+) {
+    AlertDialog(
+        onDismissRequest = onDismiss,
+        title = {
+            Text(
+                text = stringResource(R.string.sync_legend_title),
+                style = MaterialTheme.typography.headlineSmall
+            )
+        },
+        text = {
+            Column(
+                verticalArrangement = Arrangement.spacedBy(12.dp)
+            ) {
+                // Optional: Kurze Einleitung
+                Text(
+                    text = stringResource(R.string.sync_legend_description),
+                    style = MaterialTheme.typography.bodyMedium,
+                    color = MaterialTheme.colorScheme.onSurfaceVariant
+                )
+                
+                HorizontalDivider()
+                
+                // ☁️✓ SYNCED
+                LegendRow(
+                    icon = Icons.Outlined.CloudDone,
+                    tint = MaterialTheme.colorScheme.primary,
+                    label = stringResource(R.string.sync_legend_synced_label),
+                    description = stringResource(R.string.sync_legend_synced_desc)
+                )
+                
+                // ☁️↻ PENDING
+                LegendRow(
+                    icon = Icons.Outlined.CloudSync,
+                    tint = MaterialTheme.colorScheme.outline,
+                    label = stringResource(R.string.sync_legend_pending_label),
+                    description = stringResource(R.string.sync_legend_pending_desc)
+                )
+                
+                // ⚠️ CONFLICT
+                LegendRow(
+                    icon = Icons.Default.Warning,
+                    tint = MaterialTheme.colorScheme.error,
+                    label = stringResource(R.string.sync_legend_conflict_label),
+                    description = stringResource(R.string.sync_legend_conflict_desc)
+                )
+                
+                // ☁️✗ LOCAL_ONLY
+                LegendRow(
+                    icon = Icons.Outlined.CloudOff,
+                    tint = MaterialTheme.colorScheme.outline,
+                    label = stringResource(R.string.sync_legend_local_only_label),
+                    description = stringResource(R.string.sync_legend_local_only_desc)
+                )
+                
+                // ☁️✗ DELETED_ON_SERVER
+                LegendRow(
+                    icon = Icons.Outlined.CloudOff,
+                    tint = MaterialTheme.colorScheme.outline.copy(alpha = 0.5f),
+                    label = stringResource(R.string.sync_legend_deleted_label),
+                    description = stringResource(R.string.sync_legend_deleted_desc)
+                )
+            }
+        },
+        confirmButton = {
+            TextButton(onClick = onDismiss) {
+                Text(stringResource(R.string.ok))
+            }
+        }
+    )
+}
+
+/**
+ * Single row in the sync status legend
+ * Shows icon + label + description
+ */
+@Composable
+private fun LegendRow(
+    icon: ImageVector,
+    tint: Color,
+    label: String,
+    description: String
+) {
+    Row(
+        verticalAlignment = Alignment.Top,
+        modifier = Modifier.fillMaxWidth()
+    ) {
+        Icon(
+            imageVector = icon,
+            contentDescription = null,  // Dekorativ, Label reicht
+            tint = tint,
+            modifier = Modifier
+                .size(20.dp)
+                .padding(top = 2.dp)
+        )
+        Spacer(modifier = Modifier.width(12.dp))
+        Column(modifier = Modifier.weight(1f)) {
+            Text(
+                text = label,
+                style = MaterialTheme.typography.bodyMedium,
+                color = MaterialTheme.colorScheme.onSurface
+            )
+            Text(
+                text = description,
+                style = MaterialTheme.typography.bodySmall,
+                color = MaterialTheme.colorScheme.onSurfaceVariant
+            )
+        }
+    }
+}

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

@@ -58,6 +58,21 @@
     <string name="sync_status_error">Synchronisierung fehlgeschlagen</string>
     <string name="sync_already_running">Synchronisierung läuft bereits</string>
     
+    <!-- 🆕 v1.8.0: Sync-Status Legende Dialog -->
+    <string name="sync_legend_button">Sync-Status Hilfe</string>
+    <string name="sync_legend_title">Sync-Status Icons</string>
+    <string name="sync_legend_description">Jede Notiz zeigt ein kleines Icon, das den Sync-Status anzeigt:</string>
+    <string name="sync_legend_synced_label">Synchronisiert</string>
+    <string name="sync_legend_synced_desc">Diese Notiz ist auf allen Geräten aktuell.</string>
+    <string name="sync_legend_pending_label">Ausstehend</string>
+    <string name="sync_legend_pending_desc">Diese Notiz hat lokale Änderungen, die noch synchronisiert werden müssen.</string>
+    <string name="sync_legend_conflict_label">Konflikt</string>
+    <string name="sync_legend_conflict_desc">Diese Notiz wurde auf mehreren Geräten gleichzeitig geändert. Die neueste Version wurde beibehalten.</string>
+    <string name="sync_legend_local_only_label">Nur lokal</string>
+    <string name="sync_legend_local_only_desc">Diese Notiz wurde noch nie mit dem Server synchronisiert.</string>
+    <string name="sync_legend_deleted_label">Auf Server gelöscht</string>
+    <string name="sync_legend_deleted_desc">Diese Notiz wurde auf einem anderen Gerät oder direkt auf dem Server gelöscht. Sie existiert noch lokal.</string>
+    
     <!-- ============================= -->
     <!-- DELETE DIALOGS                -->
     <!-- ============================= -->

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

@@ -65,6 +65,21 @@
     <string name="sync_status_local_only">Not yet synced</string>
     <string name="sync_status_deleted_on_server">Deleted on server</string>
     
+    <!-- 🆕 v1.8.0: Sync Status Legend Dialog -->
+    <string name="sync_legend_button">Sync status help</string>
+    <string name="sync_legend_title">Sync Status Icons</string>
+    <string name="sync_legend_description">Each note shows a small icon indicating its sync status:</string>
+    <string name="sync_legend_synced_label">Synced</string>
+    <string name="sync_legend_synced_desc">This note is up to date on all devices.</string>
+    <string name="sync_legend_pending_label">Pending</string>
+    <string name="sync_legend_pending_desc">This note has local changes waiting to be synced.</string>
+    <string name="sync_legend_conflict_label">Conflict</string>
+    <string name="sync_legend_conflict_desc">This note was changed on multiple devices simultaneously. The latest version was kept.</string>
+    <string name="sync_legend_local_only_label">Local only</string>
+    <string name="sync_legend_local_only_desc">This note has never been synced to the server yet.</string>
+    <string name="sync_legend_deleted_label">Deleted on server</string>
+    <string name="sync_legend_deleted_desc">This note was deleted on another device or directly on the server. It still exists locally.</string>
+    
     <!-- ============================= -->
     <!-- DELETE DIALOGS                -->
     <!-- ============================= -->