v2.55.3 — Code-Review-Fixes: foregroundServiceType (Android 14+), POST_NOTIFICATIONS-Check, FG-Service-Notification-Channel, try/catch _zeigeSyncNotification

CRITICAL:
- AndroidManifest: foregroundServiceType="dataSync" für BackgroundService (Android 14+ MissingForegroundServiceTypeException)
- main.dart: notificationChannelId + initialNotificationTitle + foregroundServiceTypes für FlutterBackgroundService (fehlende FG-Notification → ANR/crash nach 5s)

MEDIUM:
- sync_service.dart: POST_NOTIFICATIONS-Permission-Check vor _starteForegroundService (Android 13+)
- sync_service.dart: try/catch um _zeigeSyncNotification (plugin-dispose-Sicherheit)

flutter analyze: clean | flutter test: 194/194 passed

lib/services/sync_service.dart

@@ -4,6 +4,7 @@ import 'package:flutter/foundation.dart';
 import 'package:path_provider/path_provider.dart';
 import 'package:shared_preferences/shared_preferences.dart';
 import 'package:flutter_local_notifications/flutter_local_notifications.dart';
+import 'package:permission_handler/permission_handler.dart';
 import 'package:flutter_background_service/flutter_background_service.dart';
 import '../database/db_helper.dart';
 import '../models/song.dart';
@@ -577,18 +578,22 @@ class SyncService {
     if (!Platform.isAndroid) return;
     final maxP = gesamt > 0 ? gesamt : 1;
     final p = aktuell > maxP ? maxP : aktuell;
-    notificationsPlugin.show(
-      id: _syncNotifyId,
-      title: 'Synchronisiere…',
-      body: gesamt > 0 ? '$aktuell / $gesamt Songs' : body,
-      notificationDetails: NotificationDetails(
-        android: syncNotificationDetails(
-          ongoing: true,
-          progress: p,
-          maxProgress: maxP,
+    try {
+      notificationsPlugin.show(
+        id: _syncNotifyId,
+        title: 'Synchronisiere…',
+        body: gesamt > 0 ? '$aktuell / $gesamt Songs' : body,
+        notificationDetails: NotificationDetails(
+          android: syncNotificationDetails(
+            ongoing: true,
+            progress: p,
+            maxProgress: maxP,
+          ),
         ),
-      ),
-    );
+      );
+    } catch (_) {
+      // Plugin kann beim App-Exit bereits disposed sein
+    }
   }
 
   /// Abschluss-Notification — tippbar (öffnet den Cloud-Tab, payload
@@ -630,9 +635,18 @@ class SyncService {
 
   /// Startet den Foreground-Service, damit der Sync auch bei Display-aus
   /// und minimierter App weiterläuft (Android-Prozess-Garantie).
+  /// v2.55.3: Prüft POST_NOTIFICATIONS-Permission (Android 13+).
+  /// Ohne diese Permission crasht der Foreground-Service innerhalb von
+  /// 5 Sekunden (Android killt Services ohne sichtbare Notification).
   Future<void> _starteForegroundService() async {
     if (!Platform.isAndroid) return;
     try {
+      // Android 13+: Benachrichtigungs-Berechtigung erforderlich
+      final status = await Permission.notification.status;
+      if (status.isDenied || status.isPermanentlyDenied) {
+        MeloLogger().aktion('foreground_sync_skip', {'grund': 'notification_denied'});
+        return;
+      }
       final svc = FlutterBackgroundService();
       final laeuft = await svc.isRunning();
       if (!laeuft) {