v2.41 — Issue #3: Musik-Download im Hintergrund (flutter_background_service)

- flutter_background_service ^5.0.0 hinzugefügt
- AndroidManifest: FOREGROUND_SERVICE_DATA_SYNC Permission
- main.dart: Background Service mit configure() initialisiert
- _onServiceStart(): Service-Callback für Foreground-Garantie
- DownloadService._startBackgroundService(): Foreground Service vor Download
- DownloadService._stopBackgroundService(): Stopp nach Batch/Single
- Integration in _resetStatus, downloadBatch, downloadVonUrl

lib/services/download_service.dart

@@ -5,6 +5,7 @@ import 'package:flutter/foundation.dart';
 import 'package:http/http.dart' as http;
 import 'package:path_provider/path_provider.dart';
 import 'package:flutter_local_notifications/flutter_local_notifications.dart';
+import 'package:flutter_background_service/flutter_background_service.dart';
 import '../models/song.dart';
 import '../database/db_helper.dart';
 import '../utils/audio_validator.dart';
@@ -66,13 +67,46 @@ class DownloadService extends ChangeNotifier {
     _aktuellerTitel = null;
     _fehler = null;
     _abbruchCompleter = Completer<void>();
+    _startBackgroundService();
     notifyListeners();
   }
 
+  /// Issue #3: Foreground Service starten – hält App im Hintergrund aktiv
+  void _startBackgroundService() {
+    try {
+      final svc = FlutterBackgroundService();
+      svc.isRunning().then((running) {
+        if (!running) {
+          svc.startService();
+        }
+      });
+      debugPrint('🔵 Background Service gestartet');
+    } catch (e) {
+      debugPrint('Background Service Start fehlgeschlagen: $e');
+    }
+  }
+
+  /// Issue #3: Foreground Service stoppen
+  void _stopBackgroundService() {
+    try {
+      final svc = FlutterBackgroundService();
+      svc.isRunning().then((running) {
+        if (running) {
+          svc.invoke('stopService');
+        }
+      });
+      debugPrint('🔴 Background Service gestoppt');
+    } catch (e) {
+      debugPrint('Background Service Stop fehlgeschlagen: $e');
+    }
+  }
+
   /// Song von YouTube herunterladen
   Future<Song?> downloadVonUrl(String url) async {
     _resetStatus();
-    return _downloadEinzeln(url);
+    final result = await _downloadEinzeln(url);
+    if (!_ladt) _stopBackgroundService();
+    return result;
   }
 
   /// Mehrere URLs/Playlists nacheinander mit Cooldown
@@ -147,6 +181,7 @@ class DownloadService extends ChangeNotifier {
     }
     notifyListeners();
     _completeNotification(erfolgreich, urls.length, abgebrochen: sollAbbrechen);
+    _stopBackgroundService();
     MeloLogger().zustand('download_batch_ende', {
       'erfolgreich': erfolgreich,
       'gesamt': urls.length,