feat(filename): add provider traceability tags

lib/providers/download_queue_provider.dart

@@ -690,6 +690,8 @@ class DownloadQueueNotifier extends Notifier<DownloadQueueState> {
     return DownloadRequestPayload(
       isrc: track.isrc ?? '',
       service: item.service,
+      downloadProvider: item.service,
+      providerTrackId: _knownProviderTrackId(track, item.service),
       spotifyId: payloadSpotifyId,
       trackName: track.name,
       artistName: track.artistName,

lib/providers/download_queue_provider_paths.dart

@@ -340,6 +340,8 @@ extension _DownloadQueuePaths on DownloadQueueNotifier {
       filenameFormat,
       _filenameMetadataForTrack(
         track,
+        provider: item.service,
+        providerTrackId: _knownProviderTrackId(track, item.service),
         quality: quality,
         qualityVariant: qualityVariant,
         playlistPosition: _validPlaylistPosition(item),
@@ -717,6 +719,8 @@ extension _DownloadQueuePaths on DownloadQueueNotifier {
 
   Map<String, dynamic> _filenameMetadataForTrack(
     Track track, {
+    required String provider,
+    required String providerTrackId,
     required String quality,
     String qualityVariant = '',
     int playlistPosition = 0,
@@ -729,10 +733,34 @@ extension _DownloadQueuePaths on DownloadQueueNotifier {
       'disc': track.discNumber ?? 0,
       'year': _extractYear(track.releaseDate) ?? '',
       'date': track.releaseDate ?? '',
+      'isrc': track.isrc ?? '',
+      'provider': provider,
+      'provider_id': providerTrackId,
       'playlist_position': playlistPosition,
       'playlistPosition': playlistPosition,
       'quality': quality,
       'quality_variant': qualityVariant,
     };
   }
+
+  String _knownProviderTrackId(Track track, String provider) {
+    final normalizedProvider = provider.trim().toLowerCase();
+    final normalizedSource = track.source?.trim().toLowerCase() ?? '';
+    final rawId = track.id.trim();
+    if (rawId.isEmpty) return '';
+
+    if (normalizedSource == normalizedProvider && normalizedSource.isNotEmpty) {
+      final separator = rawId.indexOf(':');
+      return separator >= 0 && separator + 1 < rawId.length
+          ? rawId.substring(separator + 1)
+          : rawId;
+    }
+
+    final separator = rawId.indexOf(':');
+    if (separator > 0 &&
+        rawId.substring(0, separator).toLowerCase() == normalizedProvider) {
+      return rawId.substring(separator + 1);
+    }
+    return '';
+  }
 }

lib/screens/settings/files_settings_page.dart

@@ -938,6 +938,9 @@ class _FilenameFormatEditorSheetState
     '{playlist_position}',
   ];
   static const _advancedTags = [
+    '{isrc}',
+    '{provider}',
+    '{provider_id}',
     '{track_raw}',
     '{track:02}',
     '{track:1}',
@@ -957,7 +960,7 @@ class _FilenameFormatEditorSheetState
     super.initState();
     _controller = TextEditingController(text: widget.initialText);
     _showAdvancedTags = RegExp(
-      r'\{(?:track_raw|disc_raw|track:\d+|disc:\d+|date:[^}]+)\}',
+      r'\{(?:isrc|provider|platform|provider_id|id|track_raw|disc_raw|track:\d+|disc:\d+|date:[^}]+)\}',
       caseSensitive: false,
     ).hasMatch(widget.initialText);
   }

lib/services/download_request_payload.dart

@@ -4,6 +4,8 @@ class DownloadRequestPayload {
   final int contractVersion;
   final String isrc;
   final String service;
+  final String downloadProvider;
+  final String providerTrackId;
   final String spotifyId;
   final String trackName;
   final String artistName;
@@ -60,6 +62,8 @@ class DownloadRequestPayload {
     this.contractVersion = nativeWorkerContractVersion,
     this.isrc = '',
     this.service = '',
+    this.downloadProvider = '',
+    this.providerTrackId = '',
     this.spotifyId = '',
     required this.trackName,
     required this.artistName,
@@ -118,6 +122,8 @@ class DownloadRequestPayload {
       'contract_version': contractVersion,
       'isrc': isrc,
       'service': service,
+      'download_provider': downloadProvider,
+      'provider_track_id': providerTrackId,
       'spotify_id': spotifyId,
       'track_name': trackName,
       'artist_name': artistName,
@@ -180,6 +186,8 @@ class DownloadRequestPayload {
       contractVersion: contractVersion,
       isrc: isrc,
       service: service,
+      downloadProvider: downloadProvider,
+      providerTrackId: providerTrackId,
       spotifyId: spotifyId,
       trackName: trackName,
       artistName: artistName,