fix: improve extension download reliability and Qobuz API integration

- Add dedicated long-timeout download client (24h) for extension file downloads,
  preventing timeouts on large lossless audio files
- Skip unnecessary SongLink Deezer prelookup when an extension download provider
  handles the track, reducing latency and avoiding spurious API failures
- Prefer native track ID over Spotify ID when a source/provider is set, ensuring
  extension providers receive their own IDs correctly
- Update Qobuz MusicDL API endpoint and switch payload URL to open.qobuz.com
- Extract buildQobuzMusicDLPayload helper and add test coverage

lib/providers/download_queue_provider.dart

@@ -3594,6 +3594,15 @@ class DownloadQueueNotifier extends Notifier<DownloadQueueState> {
       String? genre;
       String? label;
       String? copyright;
+      final extensionState = ref.read(extensionProvider);
+      final selectedExtensionDownloadProvider =
+          settings.useExtensionProviders &&
+          extensionState.extensions.any(
+            (e) =>
+                e.enabled &&
+                e.hasDownloadProvider &&
+                e.id.toLowerCase() == item.service.toLowerCase(),
+          );
 
       String? deezerTrackId = trackToDownload.deezerId;
       if (deezerTrackId == null && trackToDownload.id.startsWith('deezer:')) {
@@ -3628,7 +3637,8 @@ class DownloadQueueNotifier extends Notifier<DownloadQueueState> {
       }
 
       // Fallback: Use SongLink to convert Spotify ID to Deezer ID
-      if (deezerTrackId == null &&
+      if (!selectedExtensionDownloadProvider &&
+          deezerTrackId == null &&
           trackToDownload.id.isNotEmpty &&
           !trackToDownload.id.startsWith('deezer:') &&
           !trackToDownload.id.startsWith('extension:')) {
@@ -3729,6 +3739,10 @@ class DownloadQueueNotifier extends Notifier<DownloadQueueState> {
         if (shouldAbortWork('during SongLink availability lookup')) {
           return;
         }
+      } else if (selectedExtensionDownloadProvider && deezerTrackId == null) {
+        _log.d(
+          'Skipping Flutter SongLink Deezer prelookup for extension provider: ${item.service}',
+        );
       }
 
       if (deezerTrackId != null && deezerTrackId.isNotEmpty) {
@@ -3756,7 +3770,6 @@ class DownloadQueueNotifier extends Notifier<DownloadQueueState> {
 
       Map<String, dynamic> result;
 
-      final extensionState = ref.read(extensionProvider);
       final hasActiveExtensions = extensionState.extensions.any(
         (e) => e.enabled,
       );

lib/providers/track_provider.dart

@@ -958,9 +958,16 @@ class TrackNotifier extends Notifier<TrackState> {
     final durationMs = _extractDurationMs(data);
 
     final itemType = data['item_type']?.toString();
+    final effectiveSource =
+        source ?? data['source']?.toString() ?? data['provider_id']?.toString();
+    final spotifyId = (data['spotify_id'] ?? '').toString();
+    final nativeId = (data['id'] ?? '').toString();
+    final preferredId = effectiveSource != null && effectiveSource.isNotEmpty
+        ? (nativeId.isNotEmpty ? nativeId : spotifyId)
+        : (spotifyId.isNotEmpty ? spotifyId : nativeId);
 
     return Track(
-      id: (data['spotify_id'] ?? data['id'] ?? '').toString(),
+      id: preferredId,
       name: (data['name'] ?? '').toString(),
       artistName: (data['artists'] ?? data['artist'] ?? '').toString(),
       albumName: (data['album_name'] ?? data['album'] ?? '').toString(),
@@ -974,10 +981,7 @@ class TrackNotifier extends Notifier<TrackState> {
       discNumber: data['disc_number'] as int?,
       releaseDate: data['release_date']?.toString(),
       totalTracks: data['total_tracks'] as int?,
-      source:
-          source ??
-          data['source']?.toString() ??
-          data['provider_id']?.toString(),
+      source: effectiveSource,
       albumType: data['album_type']?.toString(),
       itemType: itemType,
     );