🚀 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

android/app/src/main/java/dev/dettmer/simplenotes/MainActivity.kt

@@ -1,19 +1,25 @@
 package dev.dettmer.simplenotes
 
 import android.Manifest
+import android.content.BroadcastReceiver
+import android.content.Context
 import android.content.Intent
+import android.content.IntentFilter
 import android.content.pm.PackageManager
 import android.os.Build
 import android.os.Bundle
+import dev.dettmer.simplenotes.utils.Logger
 import android.view.Menu
 import android.view.MenuItem
 import androidx.appcompat.app.AppCompatActivity
+import androidx.localbroadcastmanager.content.LocalBroadcastManager
 import androidx.recyclerview.widget.LinearLayoutManager
 import androidx.recyclerview.widget.RecyclerView
 import com.google.android.material.appbar.MaterialToolbar
 import com.google.android.material.floatingactionbutton.FloatingActionButton
 import dev.dettmer.simplenotes.adapters.NotesAdapter
 import dev.dettmer.simplenotes.storage.NotesStorage
+import dev.dettmer.simplenotes.sync.SyncWorker
 import dev.dettmer.simplenotes.utils.NotificationHelper
 import dev.dettmer.simplenotes.utils.showToast
 import android.widget.TextView
@@ -34,9 +40,28 @@ class MainActivity : AppCompatActivity() {
     private val storage by lazy { NotesStorage(this) }
     
     companion object {
+        private const val TAG = "MainActivity"
         private const val REQUEST_NOTIFICATION_PERMISSION = 1001
     }
     
+    /**
+     * BroadcastReceiver für Background-Sync Completion
+     */
+    private val syncCompletedReceiver = object : BroadcastReceiver() {
+        override fun onReceive(context: Context?, intent: Intent?) {
+            val success = intent?.getBooleanExtra("success", false) ?: false
+            val count = intent?.getIntExtra("count", 0) ?: 0
+            
+            Logger.d(TAG, "📡 Sync completed broadcast received: success=$success, count=$count")
+            
+            // UI refresh
+            if (success && count > 0) {
+                loadNotes()
+                Logger.d(TAG, "🔄 Notes reloaded after background sync")
+            }
+        }
+    }
+    
     override fun onCreate(savedInstanceState: Bundle?) {
         super.onCreate(savedInstanceState)
         setContentView(R.layout.activity_main)
@@ -56,9 +81,25 @@ class MainActivity : AppCompatActivity() {
     
     override fun onResume() {
         super.onResume()
+        
+        // Register BroadcastReceiver für Background-Sync
+        LocalBroadcastManager.getInstance(this).registerReceiver(
+            syncCompletedReceiver,
+            IntentFilter(SyncWorker.ACTION_SYNC_COMPLETED)
+        )
+        Logger.d(TAG, "📡 BroadcastReceiver registered")
+        
         loadNotes()
     }
     
+    override fun onPause() {
+        super.onPause()
+        
+        // Unregister BroadcastReceiver
+        LocalBroadcastManager.getInstance(this).unregisterReceiver(syncCompletedReceiver)
+        Logger.d(TAG, "📡 BroadcastReceiver unregistered")
+    }
+    
     private fun findViews() {
         recyclerViewNotes = findViewById(R.id.recyclerViewNotes)
         textViewEmpty = findViewById(R.id.textViewEmpty)