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

app/repositories/playlist.py

@@ -9,6 +9,7 @@ from sqlmodel import select
 from sqlmodel.ext.asyncio.session import AsyncSession
 
 from app.core.logging import get_logger
+from app.models.favorite import Favorite
 from app.models.playlist import Playlist
 from app.models.playlist_sound import PlaylistSound
 from app.models.sound import Sound
@@ -340,6 +341,8 @@ class PlaylistRepository(BaseRepository[Playlist]):
         include_stats: bool = False,  # noqa: FBT001, FBT002
         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."""
         try:
@@ -387,6 +390,15 @@ class PlaylistRepository(BaseRepository[Playlist]):
                 if user_id is not None:
                     subquery = subquery.where(Playlist.user_id == user_id)
 
+                # Apply favorites filter
+                if favorites_only and current_user_id is not None:
+                    # Use EXISTS subquery to avoid JOIN conflicts with GROUP BY
+                    favorites_subquery = select(1).select_from(Favorite).where(
+                        Favorite.user_id == current_user_id,
+                        Favorite.playlist_id == Playlist.id,
+                    )
+                    subquery = subquery.where(favorites_subquery.exists())
+
                 # Apply sorting
                 if sort_by == PlaylistSortField.SOUND_COUNT:
                     if sort_order == SortOrder.DESC:
@@ -449,6 +461,15 @@ class PlaylistRepository(BaseRepository[Playlist]):
                 if user_id is not None:
                     subquery = subquery.where(Playlist.user_id == user_id)
 
+                # Apply favorites filter
+                if favorites_only and current_user_id is not None:
+                    # Use EXISTS subquery to avoid JOIN conflicts with GROUP BY
+                    favorites_subquery = select(1).select_from(Favorite).where(
+                        Favorite.user_id == current_user_id,
+                        Favorite.playlist_id == Playlist.id,
+                    )
+                    subquery = subquery.where(favorites_subquery.exists())
+
                 # Apply sorting
                 if sort_by:
                     if sort_by == PlaylistSortField.NAME: