feat: Enhance favorites functionality; add favorites filtering to playlists and sounds, and improve favorite indicators in responses

app/services/playlist.py

@@ -246,6 +246,8 @@ class PlaylistService:
         include_stats: bool = False,
         limit: int | None = None,
         offset: int = 0,
+        favorites_only: bool = False,
+        current_user_id: int | None = None,
     ) -> list[dict]:
         """Search and sort playlists with optional statistics."""
         return await self.playlist_repo.search_and_sort(
@@ -256,6 +258,8 @@ class PlaylistService:
             include_stats=include_stats,
             limit=limit,
             offset=offset,
+            favorites_only=favorites_only,
+            current_user_id=current_user_id,
         )
 
     async def get_playlist_sounds(self, playlist_id: int) -> list[Sound]: