🚀 feat: Production release preparation with GitHub Actions deployment

## Major Features
- ✅ Battery optimized auto-sync (30 min interval, ~0.4%/day)
- ✅ BuildConfig.DEBUG conditional logging (Logger.kt)
- ✅ Settings UI cleanup (SSID field removed)
- ✅ Interactive notifications (click opens app)
- ✅ Post-reboot auto-sync (BootReceiver)
- ✅ GitHub Actions deployment workflow

## Implementation Details

### Auto-Sync Architecture
- WorkManager PeriodicWorkRequest (30 min intervals)
- Gateway IP detection via network interface enumeration
- Smart sync only when on home network
- BootReceiver restarts monitoring after device reboot

### Logging System
- Logger.kt object with BuildConfig.DEBUG checks
- Debug logs only in DEBUG builds
- Error/warning logs always visible
- All components updated (NetworkMonitor, SyncWorker, WebDavSyncService, etc.)

### UI Improvements
- Removed confusing SSID field from Settings
- Gateway detection fully automatic
- Material Design 3 info boxes
- Cleaner, simpler user interface

### Notifications
- PendingIntent opens MainActivity on click
- setAutoCancel(true) for auto-dismiss
- Broadcast receiver for UI refresh on sync

### GitHub Actions
- Automated APK builds on push to main
- Signed releases with proper keystore
- 3 APK variants (universal, arm64-v8a, armeabi-v7a)
- Semantic versioning: YYYY.MM.DD + build number
- Comprehensive release notes with installation guide

## Documentation
- README.md: User-friendly German guide
- DOCS.md: Technical architecture documentation
- GITHUB_ACTIONS_SETUP.md: Deployment setup guide

## Build Configuration
- Signing support via key.properties
- APK splits for smaller downloads
- ProGuard enabled with resource shrinking
- BuildConfig generation for DEBUG flag

.gitignore

@@ -15,6 +15,11 @@ android/*.apk
 android/*.ap_
 android/*.aab
 
+# Signing files (NEVER commit these!)
+android/key.properties
+android/app/*.jks
+android/app/*.keystore
+
 # Gradle
 .gradle
 build/