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

snake/loop.go

@@ -61,16 +61,16 @@ func (si *SnakeGameInstance) countdownPhase() {
 				si.initGame()
 				si.game.Status = StatusInProgress
 
-				if si.persister != nil {
-					si.persister.SaveSnakeGame(si.game)
+				if si.queries != nil {
+					si.saveSnakeGame(si.game)
 				}
 				si.gameMu.Unlock()
 				si.notify()
 				return
 			}
 
-			if si.persister != nil {
-				si.persister.SaveSnakeGame(si.game)
+			if si.queries != nil {
+				si.saveSnakeGame(si.game)
 			}
 			si.gameMu.Unlock()
 			si.notify()
@@ -123,8 +123,8 @@ func (si *SnakeGameInstance) gamePhase() {
 			// Inactivity timeout
 			if time.Since(lastInput) > inactivityLimit {
 				si.game.Status = StatusFinished
-				if si.persister != nil {
-					si.persister.SaveSnakeGame(si.game)
+				if si.queries != nil {
+					si.saveSnakeGame(si.game)
 				}
 				si.gameMu.Unlock()
 				si.notify()
@@ -195,8 +195,8 @@ func (si *SnakeGameInstance) gamePhase() {
 				si.game.Status = StatusFinished
 			}
 
-			if si.persister != nil {
-				si.persister.SaveSnakeGame(si.game)
+			if si.queries != nil {
+				si.saveSnakeGame(si.game)
 			}
 
 			si.gameMu.Unlock()