Fix critical bug and deprecation warnings

- Fixed bug in games_router.py: player_result -> player_stmt in create_game
- Updated main.py lifespan from generator to @asynccontextmanager (FastAPI deprecation)
- security.py already uses datetime.now(timezone.utc) - no change needed
- All 28 tests pass

backend/app/main.py

@@ -15,7 +15,7 @@ Mounts all consolidated routers and provides centralized configuration.
 """
 import asyncio
 import logging
-from typing import AsyncGenerator
+from contextlib import asynccontextmanager
 
 from fastapi import FastAPI
 from fastapi.middleware.cors import CORSMiddleware
@@ -36,7 +36,8 @@ from app.core.logging import configure_logging
 logger = logging.getLogger(__name__)
 
 
-def lifespan(app: FastAPI) -> AsyncGenerator[None, None]:
+@asynccontextmanager
+async def lifespan(app: FastAPI):
     """Application lifespan events for startup and shutdown."""
     config = get_config()