feat: add type static playlist

app/Models/MusicCategory.php

@@ -8,6 +8,9 @@
 use Illuminate\Database\Eloquent\Relations\HasMany;    // ← Add this
 class MusicCategory extends Model
 {
+    // Static type so playlist categories are tagged like media categories.
+    public const TYPE = 'playlist';
+
     protected $table = 'music_categories';
 
     protected $fillable = [
@@ -19,6 +22,13 @@ class MusicCategory extends Model
         'order' => 'integer',
     ];
 
+    protected $appends = ['type'];
+
+    public function getTypeAttribute(): string
+    {
+        return self::TYPE;
+    }
+
     public function playlists(): BelongsToMany
     {
         return $this->belongsToMany(MusicPlaylist::class, 'music_category_playlist', 'category_id', 'playlist_id');