refactor: remove persister abstraction layer

Inline persistence logic directly into game stores and handlers:
- game/persist.go: DB mapping methods on GameStore and GameInstance
- snake/persist.go: DB mapping methods on SnakeStore and SnakeGameInstance
- Chat persistence inlined into c4game handlers
- Delete db/persister.go (GamePersister, SnakePersister, ChatPersister)
- Stores now take *repository.Queries directly instead of Persister interface

main.go

@@ -71,20 +71,16 @@ func run(ctx context.Context) error {
 	defer cleanupNATS()
 
 	// Game stores
-	store := game.NewGameStore()
-	store.SetPersister(db.NewGamePersister(queries))
+	store := game.NewGameStore(queries)
 	store.SetNotifyFunc(func(gameID string) {
 		nc.Publish("game."+gameID, nil) //nolint:errcheck // best-effort notification
 	})
 
-	snakeStore := snake.NewSnakeStore()
-	snakeStore.SetPersister(db.NewSnakePersister(queries))
+	snakeStore := snake.NewSnakeStore(queries)
 	snakeStore.SetNotifyFunc(func(gameID string) {
 		nc.Publish("snake."+gameID, nil) //nolint:errcheck // best-effort notification
 	})
 
-	chatPersister := db.NewChatPersister(queries)
-
 	// Router
 	logger := log.Logger
 	r := chi.NewMux()
@@ -94,7 +90,7 @@ func run(ctx context.Context) error {
 		sessionManager.LoadAndSave,
 	)
 
-	if err := router.SetupRoutes(r, queries, sessionManager, nc, store, snakeStore, chatPersister, assets); err != nil {
+	if err := router.SetupRoutes(r, queries, sessionManager, nc, store, snakeStore, assets); err != nil {
 		return fmt.Errorf("setting up routes: %w", err)
 	}