feat: add totalTracks to Track model and refine EP/single classification (#202)

lib/models/track.dart

@@ -21,6 +21,7 @@ class Track {
   final ServiceAvailability? availability;
   final String? source;
   final String? albumType;
+  final int? totalTracks;
   final String? itemType;
 
   const Track({
@@ -41,10 +42,21 @@ class Track {
     this.availability,
     this.source,
     this.albumType,
+    this.totalTracks,
     this.itemType,
   });
 
-  bool get isSingle => albumType == 'single' || albumType == 'ep';
+  bool get isSingle {
+    switch (albumType?.toLowerCase()) {
+      case 'single':
+        return true;
+      case 'ep':
+        final count = totalTracks;
+        return count == null || count <= 1;
+      default:
+        return false;
+    }
+  }
   
   bool get isAlbumItem => itemType == 'album';
   

lib/models/track.g.dart

@@ -28,6 +28,7 @@ Track _$TrackFromJson(Map<String, dynamic> json) => Track(
         ),
   source: json['source'] as String?,
   albumType: json['albumType'] as String?,
+  totalTracks: (json['totalTracks'] as num?)?.toInt(),
   itemType: json['itemType'] as String?,
 );
 
@@ -49,6 +50,7 @@ Map<String, dynamic> _$TrackToJson(Track instance) => <String, dynamic>{
   'availability': instance.availability,
   'source': instance.source,
   'albumType': instance.albumType,
+  'totalTracks': instance.totalTracks,
   'itemType': instance.itemType,
 };