perf(battlesnake): defer ordered lifecycle bookkeeping

- Acknowledge start and end without waiting for persistence or dashboards.
- Keep runtime creation and finished-game removal on the response path.
- Serialize start, turn, and end bookkeeping per game in Quart tasks.
- Capture turn thinking before scheduling deferred persistence.
- Defer start metrics, logging, and stale-game pruning.
- Run legacy history exports in a worker thread.
- Record results and end metrics even when history export fails.
- Drain pending bookkeeping before closing storage during shutdown.
- Test sub-500 ms responses with slow backends and real SQLite.
- Cover event ordering, export failures, and rejected user agents.

server/services/gameplay_tracking.py

@@ -23,10 +23,13 @@ class GameplayTrackingService:
       await await_log(self.logger.warning(f"Gameplay DB start record failed:{error}"))
 
   async def record_gameplay_turn(self, game_state:dict, my_move:str, game_board:GameBoard) -> None:
+    thinking = self._extract_latest_snake_thinking(game_board)
+    await self.record_gameplay_turn_snapshot(game_state, my_move, thinking)
+
+  async def record_gameplay_turn_snapshot(self, game_state:dict, my_move:str|None, thinking:dict|None) -> None:
     if self.gameplay_database is None:
       return
     try:
-      thinking = self._extract_latest_snake_thinking(game_board)
       await self.gameplay_database.record_turn(game_state, my_move, thinking)
     except Exception as error:
       await await_log(self.logger.warning(f"Gameplay DB turn record failed:{error}"))