fix(app): 곡 상세 화면 뮤직비디오 표시 안 되는 문제 수정

TrackDetail.fromJson에서 music_video_url → video_url로 필드명 수정.
DB 컬럼명은 video_url인데 잘못된 키로 파싱하고 있었음.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

app/lib/models/album.dart

@@ -214,6 +214,7 @@ class TrackDetail {
   final String? arranger;
   final String? lyrics;
   final String? musicVideoUrl;
+  final String? videoType;
   final TrackAlbum? album;
 
   TrackDetail({
@@ -227,6 +228,7 @@ class TrackDetail {
     this.arranger,
     this.lyrics,
     this.musicVideoUrl,
+    this.videoType,
     this.album,
   });
 
@@ -241,7 +243,8 @@ class TrackDetail {
       composer: json['composer'] as String?,
       arranger: json['arranger'] as String?,
       lyrics: json['lyrics'] as String?,
-      musicVideoUrl: json['music_video_url'] as String?,
+      musicVideoUrl: json['video_url'] as String?,
+      videoType: json['video_type'] as String?,
       album: json['album'] != null ? TrackAlbum.fromJson(json['album']) : null,
     );
   }