feat: add separate filename format for singles and EPs (#271)

Add singleFilenameFormat setting so singles/EPs can use a different filename template than albums. The format editor is reused with custom title/description. Dart selects the correct format based on track.isSingle before passing to Go, so no backend changes needed. Also fix isSingle getter to include all EPs regardless of totalTracks. Closes #271

lib/models/settings.dart

@@ -35,6 +35,7 @@ class AppSettings {
   final String? searchProvider;
   final String? homeFeedProvider;
   final bool separateSingles;
+  final String singleFilenameFormat;
   final String albumFolderStructure;
   final bool showExtensionStore;
   final String locale;
@@ -108,6 +109,7 @@ class AppSettings {
     this.searchProvider,
     this.homeFeedProvider,
     this.separateSingles = false,
+    this.singleFilenameFormat = '{title} - {artist}',
     this.albumFolderStructure = 'artist_album',
     this.showExtensionStore = true,
     this.locale = 'system',
@@ -170,6 +172,7 @@ class AppSettings {
     String? homeFeedProvider,
     bool clearHomeFeedProvider = false,
     bool? separateSingles,
+    String? singleFilenameFormat,
     String? albumFolderStructure,
     bool? showExtensionStore,
     String? locale,
@@ -232,6 +235,7 @@ class AppSettings {
           ? null
           : (homeFeedProvider ?? this.homeFeedProvider),
       separateSingles: separateSingles ?? this.separateSingles,
+      singleFilenameFormat: singleFilenameFormat ?? this.singleFilenameFormat,
       albumFolderStructure: albumFolderStructure ?? this.albumFolderStructure,
       showExtensionStore: showExtensionStore ?? this.showExtensionStore,
       locale: locale ?? this.locale,

lib/models/settings.g.dart

@@ -15,7 +15,7 @@ AppSettings _$AppSettingsFromJson(Map<String, dynamic> json) => AppSettings(
   downloadTreeUri: json['downloadTreeUri'] as String? ?? '',
   autoFallback: json['autoFallback'] as bool? ?? true,
   embedMetadata: json['embedMetadata'] as bool? ?? true,
-  artistTagMode: json['artistTagMode'] as String? ?? 'joined',
+  artistTagMode: json['artistTagMode'] as String? ?? artistTagModeJoined,
   embedLyrics: json['embedLyrics'] as bool? ?? true,
   maxQualityCover: json['maxQualityCover'] as bool? ?? true,
   isFirstLaunch: json['isFirstLaunch'] as bool? ?? true,
@@ -37,6 +37,8 @@ AppSettings _$AppSettingsFromJson(Map<String, dynamic> json) => AppSettings(
   searchProvider: json['searchProvider'] as String?,
   homeFeedProvider: json['homeFeedProvider'] as String?,
   separateSingles: json['separateSingles'] as bool? ?? false,
+  singleFilenameFormat:
+      json['singleFilenameFormat'] as String? ?? '{title} - {artist}',
   albumFolderStructure:
       json['albumFolderStructure'] as String? ?? 'artist_album',
   showExtensionStore: json['showExtensionStore'] as bool? ?? true,
@@ -104,6 +106,7 @@ Map<String, dynamic> _$AppSettingsToJson(
   'searchProvider': instance.searchProvider,
   'homeFeedProvider': instance.homeFeedProvider,
   'separateSingles': instance.separateSingles,
+  'singleFilenameFormat': instance.singleFilenameFormat,
   'albumFolderStructure': instance.albumFolderStructure,
   'showExtensionStore': instance.showExtensionStore,
   'locale': instance.locale,

lib/models/track.dart

@@ -49,26 +49,24 @@ class Track {
   bool get isSingle {
     switch (albumType?.toLowerCase()) {
       case 'single':
-        return true;
       case 'ep':
-        final count = totalTracks;
-        return count == null || count <= 1;
+        return true;
       default:
         return false;
     }
   }
-  
+
   bool get isAlbumItem => itemType == 'album';
-  
+
   bool get isPlaylistItem => itemType == 'playlist';
-  
+
   bool get isArtistItem => itemType == 'artist';
-  
+
   bool get isCollection => isAlbumItem || isPlaylistItem || isArtistItem;
 
   factory Track.fromJson(Map<String, dynamic> json) => _$TrackFromJson(json);
   Map<String, dynamic> toJson() => _$TrackToJson(this);
-  
+
   bool get isFromExtension => source != null && source!.isNotEmpty;
 }