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/models/user.py

@@ -8,6 +8,7 @@ from app.models.base import BaseModel
 if TYPE_CHECKING:
     from app.models.credit_transaction import CreditTransaction
     from app.models.extraction import Extraction
+    from app.models.favorite import Favorite
     from app.models.plan import Plan
     from app.models.playlist import Playlist
     from app.models.sound_played import SoundPlayed
@@ -37,3 +38,4 @@ class User(BaseModel, table=True):
     sounds_played: list["SoundPlayed"] = Relationship(back_populates="user")
     extractions: list["Extraction"] = Relationship(back_populates="user")
     credit_transactions: list["CreditTransaction"] = Relationship(back_populates="user")
+    favorites: list["Favorite"] = Relationship(back_populates="user")