fix: offline mode migration bug for v1.5.0 → v1.6.2 updates

- Fixes offline mode incorrectly enabled after updating from v1.5.0
- Users with existing server configuration no longer appear as offline
- Root cause: KEY_OFFLINE_MODE didn't exist in v1.5.0
- MainViewModel/NoteEditorViewModel used hardcoded default 'true'
- Fix: Migration in SimpleNotesApplication.onCreate() detects server config
- Version bumped to v1.6.2 (versionCode 16)
- F-Droid changelogs added

Tested: v1.5.0 → v1.6.2 update successful
Migration log: hasServer=true → offlineMode=false ✓

android/app/build.gradle.kts

@@ -20,8 +20,8 @@ android {
         applicationId = "dev.dettmer.simplenotes"
         minSdk = 24
         targetSdk = 36
-        versionCode = 15  // 🔧 v1.6.1: Lint-Cleanup detekt and ktlint
-        versionName = "1.6.1"  // 🔧 v1.6.1: Lint-Cleanup detekt and ktlint
+        versionCode = 16  // 🔧 v1.6.2: Hotfix offline mode migration bug
+        versionName = "1.6.2"  // 🔧 v1.6.2: Hotfix offline mode migration bug
 
         testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
     }