Fix mobile app submodule initialization and cleanup

- Removed incorrect swingmusic_mobile directory
- Properly initialized swingmusic_mobile submodule from swingmusic-mobile.git
- Clean submodule configuration for unified release workflow

swingmusic_mobile/lib/data/models/artist_model.dart

@@ -1,96 +0,0 @@
-import 'package:equatable/equatable.dart';
-import 'album_model.dart';
-import 'track_model.dart';
-
-class ArtistModel extends Equatable {
-  final String name;
-  final String artisthash;
-  final String image;
-  final int trackcount;
-  final int albumcount;
-  final int duration;
-  final int lastplayed;
-  final int playcount;
-  final int playduration;
-  final List<int> favUserids;
-  final bool isFavorite;
-  final List<AlbumModel> albums;
-  final List<TrackModel> tracks;
-
-  const ArtistModel({
-    required this.name,
-    required this.artisthash,
-    this.image = '',
-    this.trackcount = 0,
-    this.albumcount = 0,
-    this.duration = 0,
-    this.lastplayed = 0,
-    this.playcount = 0,
-    this.playduration = 0,
-    this.favUserids = const [],
-    this.isFavorite = false,
-    this.albums = const [],
-    this.tracks = const [],
-  });
-
-  ArtistModel copyWith({
-    String? name,
-    String? artisthash,
-    String? image,
-    int? trackcount,
-    int? albumcount,
-    int? duration,
-    int? lastplayed,
-    int? playcount,
-    int? playduration,
-    List<int>? favUserids,
-    bool? isFavorite,
-    List<AlbumModel>? albums,
-    List<TrackModel>? tracks,
-  }) {
-    return ArtistModel(
-      name: name ?? this.name,
-      artisthash: artisthash ?? this.artisthash,
-      image: image ?? this.image,
-      trackcount: trackcount ?? this.trackcount,
-      albumcount: albumcount ?? this.albumcount,
-      duration: duration ?? this.duration,
-      lastplayed: lastplayed ?? this.lastplayed,
-      playcount: playcount ?? this.playcount,
-      playduration: playduration ?? this.playduration,
-      favUserids: favUserids ?? this.favUserids,
-      isFavorite: isFavorite ?? this.isFavorite,
-      albums: albums ?? this.albums,
-      tracks: tracks ?? this.tracks,
-    );
-  }
-
-  @override
-  List<Object?> get props => [
-        name,
-        artisthash,
-        image,
-        trackcount,
-        albumcount,
-        duration,
-        lastplayed,
-        playcount,
-        playduration,
-        favUserids,
-        isFavorite,
-        albums,
-        tracks,
-      ];
-
-  String get durationFormatted {
-    final hours = duration ~/ 3600;
-    final minutes = (duration % 3600) ~/ 60;
-    final seconds = duration % 60;
-    
-    if (hours > 0) {
-      return '${hours}:${minutes.toString().padLeft(2, '0')}:${seconds.toString().padLeft(2, '0')}';
-    } else {
-      return '${minutes.toString().padLeft(2, '0')}:${seconds.toString().padLeft(2, '0')}';
-    }
-  }
-}