📊 Feature: History-Sync vom Navidrome-Server (Phase 2, Part 5/X)

- Neue NavidromeService APIs: scrobble() + getBookmark()
- Lädt Wiedergabe-Position vom Server beim Song-Start (Subsonic-API)
- Sendet Position alle 5s zum Server wenn verbunden
- Priorisiert Server-Position über lokale Position
- Full Sync: lokal speichern + Server synchen parallel

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XJzQjUtnvYUtHdnTs3iCru

lib/services/navidrome_service.dart

@@ -298,6 +298,49 @@ class NavidromeService {
       return streamUrl(songId);
     }
   }
+
+  /// Speichert die aktuelle Wiedergabe-Position für einen Song zum Server.
+  /// Subsonic-API: scrobble.view mit `submission=true` und Position in Sekunden.
+  Future<void> scrobble(String songId, int positionSeconds) async {
+    if (!istVerbunden) return;
+    try {
+      final uri = _uri('scrobble.view', {
+        'id': songId,
+        'submission': 'true',
+        'position': positionSeconds.toString(),
+      });
+      await http.get(uri).timeout(const Duration(seconds: 10));
+      debugPrint('Scrobble erfolgreich: Song=$songId, Position=${positionSeconds}s');
+    } catch (e) {
+      debugPrint('Scrobble Fehler: $e');
+    }
+  }
+
+  /// Lädt die gespeicherte Wiedergabe-Position für einen Song vom Server.
+  /// Gibt Position in Millisekunden zurück oder null wenn nicht gespeichert.
+  Future<int?> getBookmark(String songId) async {
+    if (!istVerbunden) return null;
+    try {
+      final uri = _uri('getBookmarks.view', {'id': songId});
+      final response = await http.get(uri).timeout(const Duration(seconds: 10));
+      if (response.statusCode != 200) return null;
+
+      final json = jsonDecode(response.body) as Map<String, dynamic>;
+      final subsonicResponse = json['subsonic-response'] as Map<String, dynamic>?;
+      if (subsonicResponse == null) return null;
+
+      final bookmarks = subsonicResponse['bookmark'] as List<dynamic>?;
+      if (bookmarks == null || bookmarks.isEmpty) return null;
+
+      final position = (bookmarks[0] as Map<String, dynamic>)['position'] as int?;
+      if (position == null) return null;
+      debugPrint('Bookmark geladen: Song=$songId, Position=${position}ms');
+      return position;
+    } catch (e) {
+      debugPrint('Bookmark Fehler: $e');
+      return null;
+    }
+  }
 }
 
 class SubsonicArtist {