refactor(models): unify table names to singular form for consistency across models

app/models/playlist_sound.py

@@ -17,14 +17,14 @@ if TYPE_CHECKING:
 class PlaylistSound(db.Model):
     """Model for playlist-sound relationships with ordering."""
 
-    __tablename__ = "playlist_sounds"
+    __tablename__ = "playlist_sound"
 
     id: Mapped[int] = mapped_column(Integer, primary_key=True)
     playlist_id: Mapped[int] = mapped_column(
-        Integer, ForeignKey("playlists.id"), nullable=False
+        Integer, ForeignKey("playlist.id"), nullable=False
     )
     sound_id: Mapped[int] = mapped_column(
-        Integer, ForeignKey("sounds.id"), nullable=False
+        Integer, ForeignKey("sound.id"), nullable=False
     )
     order: Mapped[int] = mapped_column(Integer, nullable=False)
     added_at: Mapped[datetime] = mapped_column(