fix(download): suffix batch filenames with track number when needed

Mark multi-track queue additions as batch downloads and append
{track:02} - {title} when the configured format has no uniqueness
token, instead of relying on playlist position alone.

lib/models/download_item.dart

@@ -38,6 +38,7 @@ class DownloadItem {
   final String? qualityOverride;
   final String? playlistName;
   final int? playlistPosition; // 1-based position in the source playlist
+  final bool fromBatch;
 
   const DownloadItem({
     required this.id,
@@ -55,6 +56,7 @@ class DownloadItem {
     this.qualityOverride,
     this.playlistName,
     this.playlistPosition,
+    this.fromBatch = false,
   });
 
   DownloadItem copyWith({
@@ -73,6 +75,7 @@ class DownloadItem {
     String? qualityOverride,
     String? playlistName,
     int? playlistPosition,
+    bool? fromBatch,
   }) {
     return DownloadItem(
       id: id ?? this.id,
@@ -90,6 +93,7 @@ class DownloadItem {
       qualityOverride: qualityOverride ?? this.qualityOverride,
       playlistName: playlistName ?? this.playlistName,
       playlistPosition: playlistPosition ?? this.playlistPosition,
+      fromBatch: fromBatch ?? this.fromBatch,
     );
   }
 

lib/models/download_item.g.dart

@@ -24,6 +24,7 @@ DownloadItem _$DownloadItemFromJson(Map<String, dynamic> json) => DownloadItem(
   qualityOverride: json['qualityOverride'] as String?,
   playlistName: json['playlistName'] as String?,
   playlistPosition: (json['playlistPosition'] as num?)?.toInt(),
+  fromBatch: json['fromBatch'] as bool? ?? false,
 );
 
 Map<String, dynamic> _$DownloadItemToJson(DownloadItem instance) =>
@@ -43,6 +44,7 @@ Map<String, dynamic> _$DownloadItemToJson(DownloadItem instance) =>
       'qualityOverride': instance.qualityOverride,
       'playlistName': instance.playlistName,
       'playlistPosition': instance.playlistPosition,
+      'fromBatch': instance.fromBatch,
     };
 
 const _$DownloadStatusEnumMap = {

lib/providers/download_queue_provider.dart

@@ -189,6 +189,10 @@ const _defaultOutputFolderName = 'SpotiFLAC';
 const _defaultAndroidMusicSubpath = 'Music/$_defaultOutputFolderName';
 const _maxSafFilenameUtf8Bytes = 180;
 const _maxSafDirSegmentUtf8Bytes = 120;
+final _batchUniqueFilenameTokenPattern = RegExp(
+  r'\{(?:title|track(?:_raw)?|track:\d+|playlist_position(?:_raw)?|playlist_position:\d+|playlist position|playlistPosition|position(?::\d+)?)\}',
+  caseSensitive: false,
+);
 
 class DownloadHistoryItem {
   final String id;
@@ -3863,6 +3867,7 @@ class DownloadQueueNotifier extends Notifier<DownloadQueueState> {
     final takenIds = state.items.map((item) => item.id).toSet();
     final shouldAssignPlaylistPositions =
         playlistName != null && playlistName.trim().isNotEmpty;
+    final fromBatch = tracks.length > 1;
     final newItems = tracks.asMap().entries.map((entry) {
       final track = entry.value;
       final index = entry.key;
@@ -3884,6 +3889,7 @@ class DownloadQueueNotifier extends Notifier<DownloadQueueState> {
         playlistPosition:
             explicitPosition ??
             (shouldAssignPlaylistPositions ? index + 1 : null),
+        fromBatch: fromBatch,
       );
     }).toList();
 
@@ -3902,19 +3908,17 @@ class DownloadQueueNotifier extends Notifier<DownloadQueueState> {
   }
 
   String _filenameFormatForItem(DownloadItem item, String baseFormat) {
-    if (_validPlaylistPosition(item) == 0 ||
-        item.playlistName == null ||
-        item.playlistName!.trim().isEmpty) {
+    if (!item.fromBatch) {
       return baseFormat;
     }
-
-    final lower = baseFormat.toLowerCase();
-    if (lower.contains('{playlist_position') ||
-        lower.contains('{playlist position') ||
-        lower.contains('{playlistposition')) {
+    final trimmed = baseFormat.trim();
+    if (trimmed.isEmpty) {
       return baseFormat;
     }
-    return '{playlist_position:02} - $baseFormat';
+    if (_batchUniqueFilenameTokenPattern.hasMatch(trimmed)) {
+      return baseFormat;
+    }
+    return '$trimmed - {track:02} - {title}';
   }
 
   Map<String, dynamic> _filenameMetadataForTrack(