feat: Implement favorites management API; add endpoints for adding, removing, and retrieving favorites for sounds and playlists

feat: Create Favorite model and repository for managing user favorites in the database
feat: Add FavoriteService to handle business logic for favorites management
feat: Enhance Playlist and Sound response schemas to include favorite indicators and counts
refactor: Update API routes to include favorites functionality in playlists and sounds

app/schemas/playlist.py

@@ -33,12 +33,23 @@ class PlaylistResponse(BaseModel):
     is_main: bool
     is_current: bool
     is_deletable: bool
+    is_favorited: bool = False
+    favorite_count: int = 0
     created_at: str
     updated_at: str | None
 
     @classmethod
-    def from_playlist(cls, playlist: Playlist) -> "PlaylistResponse":
-        """Create response from playlist model."""
+    def from_playlist(cls, playlist: Playlist, is_favorited: bool = False, favorite_count: int = 0) -> "PlaylistResponse":
+        """Create response from playlist model.
+        
+        Args:
+            playlist: The Playlist model
+            is_favorited: Whether the playlist is favorited by the current user
+            favorite_count: Number of users who favorited this playlist
+            
+        Returns:
+            PlaylistResponse instance
+        """
         if playlist.id is None:
             msg = "Playlist ID cannot be None"
             raise ValueError(msg)
@@ -50,6 +61,8 @@ class PlaylistResponse(BaseModel):
             is_main=playlist.is_main,
             is_current=playlist.is_current,
             is_deletable=playlist.is_deletable,
+            is_favorited=is_favorited,
+            favorite_count=favorite_count,
             created_at=playlist.created_at.isoformat(),
             updated_at=playlist.updated_at.isoformat() if playlist.updated_at else None,
         )