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/Server.py

@@ -21,6 +21,7 @@ from server.blueprints import (
   create_metrics_blueprint,
   create_dashboard_blueprint,
 )
+from server.services.game_lifecycle import GameLifecycleService
 from server.services import (
   DashboardEventsService,
   DashboardWebSocketHub,
@@ -106,6 +107,7 @@ class Server:
 
     self.app = Quart('Battlesnake', template_folder=os.path.join(data_path, 'templates', 'side'), static_folder=os.path.join(data_path, 'templates', 'files'))
 
+    self.game_lifecycle = GameLifecycleService(self)
     self.app.register_blueprint(create_battlesnake_blueprint(self))
     self.app.register_blueprint(create_metrics_blueprint(self))
     self.app.register_blueprint(create_dashboard_blueprint(self))
@@ -143,6 +145,7 @@ class Server:
 
     @self.app.after_serving
     async def shutdown_state_storage():
+      await self.game_lifecycle.drain()
       await self.dashboard_events_service.stop_listener()
       await self.metrics_collector.close()
       if self.gameplay_database is not None: