v2.35 — Vollständiges Sync-System: Playlisten, Favoriten, Auto-Sync, Persistent Login, Benutzerdefinierte Namen

## Server (melo_cloud.py v3.0.0)
- Neue DB-Tabellen: user_playlists, user_playlist_songs, user_favorites, user_history, sync_meta
- Playlist-Endpunkte: GET/POST /api/cloud/playlists, GET /api/cloud/playlists/<id>, POST songs, DELETE songs, PUT positions
- Favoriten-Endpunkte: GET/POST /api/cloud/favorites, POST /api/cloud/favorites/toggle
- History-Endpunkte: GET/POST /api/cloud/history (mit Dedup)
- Rename-Endpunkt: POST /api/cloud/rename (custom_title/custom_artist)
- Sync-Endpunkte: POST /api/cloud/sync-all, GET /api/cloud/sync-status
- delete-all erweitert um Playlists + Favorites + History

## App
- db_helper.dart: Migration v4→v5 (cloud_id, cloud_title, cloud_artist, server_favorites, sync_metadata)
- auth_service.dart: Token-Validierung beim Start (online check + Offline-Fallback), Persistent Login
- cloud_service.dart: Neue Methoden für Playlists (CRUD), Favorites (get/sync/toggle), Rename, History, syncAll/syncStatus
- cloud_screen.dart: Komplett-Rewrite mit Sync-Modus (Manuell/Auto), Intervall-Auswahl, Sync-Fortschritt-Anzeige, Playlist-Verwaltung, Favoriten-Anzeige + Umbenennen, Sync-Info-Karte, nächster Sync
- main.dart: Auto-Sync beim App-Start (nur wenn konfiguriert + fällig)

## Flutter Analyze
- 0 neue Issues — nur 7 pre-existing

lib/database/db_helper.dart

@@ -20,7 +20,7 @@ class DbHelper {
     final pfad = await getDatabasesPath();
     return openDatabase(
       p.join(pfad, 'melo.db'),
-      version: 4,
+      version: 5,
       onCreate: (db, version) async {
         await db.execute('''
           CREATE TABLE songs (
@@ -107,6 +107,33 @@ class DbHelper {
             // Spalte existiert bereits – ignorieren
           }
         }
+        if (oldVersion < 5) {
+          try {
+            await db.execute('ALTER TABLE songs ADD COLUMN cloud_id TEXT');
+          } catch (_) {}
+          try {
+            await db.execute('ALTER TABLE songs ADD COLUMN cloud_title TEXT');
+          } catch (_) {}
+          try {
+            await db.execute('ALTER TABLE songs ADD COLUMN cloud_artist TEXT');
+          } catch (_) {}
+          try {
+            await db.execute('''
+              CREATE TABLE IF NOT EXISTS server_favorites (
+                cloud_id TEXT PRIMARY KEY,
+                favorited_at TEXT
+              )
+            ''');
+          } catch (_) {}
+          try {
+            await db.execute('''
+              CREATE TABLE IF NOT EXISTS sync_metadata (
+                key TEXT PRIMARY KEY,
+                value TEXT
+              )
+            ''');
+          } catch (_) {}
+        }
       },
     );
   }
@@ -356,6 +383,73 @@ class DbHelper {
     return rows.map((r) => Song.fromMap(r)).toList();
   }
 
+  /// Cloud-ID für einen Song speichern (Verknüpfung lokal ↔ Cloud)
+  Future<void> cloudIdSetzen(int songId, String cloudId,
+      {String? cloudTitle, String? cloudArtist}) async {
+    final d = await db;
+    final update = <String, dynamic>{'cloud_id': cloudId};
+    if (cloudTitle != null) update['cloud_title'] = cloudTitle;
+    if (cloudArtist != null) update['cloud_artist'] = cloudArtist;
+    await d.update('songs', update, where: 'id = ?', whereArgs: [songId]);
+  }
+
+  /// Sync-Metadaten lesen
+  Future<String?> syncMetaGet(String key) async {
+    final d = await db;
+    final rows = await d.query('sync_metadata',
+        where: 'key = ?', whereArgs: [key]);
+    if (rows.isEmpty) return null;
+    return rows.first['value'] as String?;
+  }
+
+  /// Sync-Metadaten setzen
+  Future<void> syncMetaSet(String key, String value) async {
+    final d = await db;
+    await d.insert('sync_metadata', {'key': key, 'value': value},
+        conflictAlgorithm: ConflictAlgorithm.replace);
+  }
+
+  /// Server-Favoriten abrufen (alle cloud_ids)
+  Future<Set<String>> serverFavoritesGet() async {
+    final d = await db;
+    final rows = await d.query('server_favorites');
+    return rows.map((r) => r['cloud_id'] as String).toSet();
+  }
+
+  /// Server-Favoriten ersetzen (komplette Liste)
+  Future<void> serverFavoritesSet(List<String> cloudIds) async {
+    final d = await db;
+    await d.transaction((txn) async {
+      await txn.delete('server_favorites');
+      final now = DateTime.now().toIso8601String();
+      for (final cid in cloudIds) {
+        await txn.insert('server_favorites',
+            {'cloud_id': cid, 'favorited_at': now});
+      }
+    });
+  }
+
+  /// Song per cloud_id finden
+  Future<Song?> songNachCloudId(String cloudId) async {
+    final d = await db;
+    final rows = await d.query('songs',
+        where: 'cloud_id = ?', whereArgs: [cloudId]);
+    if (rows.isEmpty) return null;
+    return Song.fromMap(rows.first);
+  }
+
+  /// Benutzerdefinierte Metadaten für Cloud-Song aktualisieren
+  Future<void> cloudMetadatenAktualisieren(int songId,
+      {String? title, String? artist}) async {
+    final d = await db;
+    final update = <String, dynamic>{};
+    if (title != null) update['cloud_title'] = title;
+    if (artist != null) update['cloud_artist'] = artist;
+    if (update.isNotEmpty) {
+      await d.update('songs', update, where: 'id = ?', whereArgs: [songId]);
+    }
+  }
+
   Future<void> loeschen() async {
     final d = await db;
     await d.transaction((txn) async {