🚀 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/build.gradle.kts

@@ -17,20 +17,55 @@ android {
         versionName = "1.0"
 
         testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
+        
+        // Enable multiple APKs per ABI for smaller downloads
+        splits {
+            abi {
+                isEnable = true
+                reset()
+                include("armeabi-v7a", "arm64-v8a")
+                isUniversalApk = true  // Also generate universal APK
+            }
+        }
+    }
+
+    // Signing configuration for release builds
+    signingConfigs {
+        create("release") {
+            // Load keystore configuration from key.properties file
+            val keystorePropertiesFile = rootProject.file("key.properties")
+            if (keystorePropertiesFile.exists()) {
+                val keystoreProperties = java.util.Properties()
+                keystoreProperties.load(java.io.FileInputStream(keystorePropertiesFile))
+                
+                storeFile = file(keystoreProperties["storeFile"] as String)
+                storePassword = keystoreProperties["storePassword"] as String
+                keyAlias = keystoreProperties["keyAlias"] as String
+                keyPassword = keystoreProperties["keyPassword"] as String
+            }
+        }
     }
 
     buildTypes {
         release {
-            isMinifyEnabled = false
+            isMinifyEnabled = true
+            isShrinkResources = true
             proguardFiles(
                 getDefaultProguardFile("proguard-android-optimize.txt"),
                 "proguard-rules.pro"
             )
+            // Use release signing config if available, otherwise debug
+            signingConfig = if (rootProject.file("key.properties").exists()) {
+                signingConfigs.getByName("release")
+            } else {
+                signingConfigs.getByName("debug")
+            }
         }
     }
 
     buildFeatures {
         viewBinding = true
+        buildConfig = true  // Enable BuildConfig generation
     }
 
     compileOptions {
@@ -59,6 +94,9 @@ dependencies {
     implementation("androidx.recyclerview:recyclerview:1.3.2")
     implementation("androidx.lifecycle:lifecycle-runtime-ktx:2.7.0")
 
+    // LocalBroadcastManager für UI Refresh
+    implementation("androidx.localbroadcastmanager:localbroadcastmanager:1.1.0")
+
     // Testing (bleiben so)
     testImplementation(libs.junit)
     androidTestImplementation(libs.androidx.junit)