feat: many category and sub can be in playlist

app/Models/MusicPlaylist.php

@@ -4,6 +4,7 @@
 
 use Illuminate\Database\Eloquent\Model;
 use Illuminate\Database\Eloquent\Relations\BelongsTo;  // ← Add this
+use Illuminate\Database\Eloquent\Relations\BelongsToMany;
 use Illuminate\Database\Eloquent\Relations\HasMany;    // ← Add this
 use App\Traits\HasComments; // Add this
 use App\Traits\HasLikes;
@@ -14,7 +15,7 @@ class MusicPlaylist extends Model
     protected $table = 'music_playlists';
     
     protected $fillable = [
-        'category_id', 'subcategory_id','name', 'slug', 'description', 'image_id', 'order', 'is_active'
+        'name', 'slug', 'description', 'image_id', 'order', 'is_active'
     ];
     
     protected $casts = [
@@ -31,14 +32,14 @@ class MusicPlaylist extends Model
         'is_saved',
         'saved_count'
     ];
-    public function category(): BelongsTo
+    public function categories(): BelongsToMany
     {
-        return $this->belongsTo(MusicCategory::class, 'category_id');
+        return $this->belongsToMany(MusicCategory::class, 'music_category_playlist', 'playlist_id', 'category_id');
     }
-    
-     public function subcategory(): BelongsTo
+
+    public function subcategories(): BelongsToMany
     {
-        return $this->belongsTo(MusicSubcategory::class, 'subcategory_id');
+        return $this->belongsToMany(MusicSubcategory::class, 'music_subcategory_playlist', 'playlist_id', 'subcategory_id');
     }