Add resource limits, abuse protection and overload handling

Running games always continue; new work is refused when there is no
capacity; abuse is rejected immediately.

- Docker: CPU/memory/pids caps per container (overridable in .env);
  uvicorn message size, queue and concurrency limits
- Server abuse limits: connections total/per IP (close 1013), message
  rate per connection (token bucket, close 1008 on floods), lobby
  creation rate per IP
- Load monitor: event loop lag, CPU of the own cgroup quota and
  throttling, with hysteresis (normal/busy/overloaded, severe lag
  overloads immediately)
- Admission control: create_lobby and start_game refused while
  overloaded or MAX_ACTIVE_GAMES are running; server_status message
  broadcast on changes; /health reports load but stays ok
- AI bridge: timeout sent with requests, in-flight cap, circuit breaker
- AI service: bounded workers and queue ("overloaded"), drops expired
  requests, degrades to the heuristic agent when busy or too slow
- Website: busy notices, Create/Start disabled when not accepting
  games, slow retry when the server is full
- Tests for limiters, load levels, admission control and AI service
  limits; docs updated

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

wizard_server/app/main.py

@@ -30,23 +30,22 @@ def create_app(config: Settings = settings) -> FastAPI:
     async def lifespan(_: FastAPI) -> AsyncIterator[None]:
         if not config.ai_shared_secret:
             logger.warning("AI_SHARED_SECRET is not set, /internal/ai is unauthenticated")
-        cleanup = asyncio.create_task(service.cleanup_loop())
+        tasks = [
+            asyncio.create_task(service.cleanup_loop()),
+            asyncio.create_task(service.load.run()),
+        ]
         try:
             yield
         finally:
-            cleanup.cancel()
+            for task in tasks:
+                task.cancel()
 
     app = FastAPI(title="Wizard game server", lifespan=lifespan, docs_url=None, redoc_url=None)
     app.state.service = service
 
     @app.get("/health")
     async def health() -> dict:
-        return {
-            "status": "ok",
-            "lobbies": len(service.lobbies),
-            "sessions": len(service.sessions),
-            "ai_available": service.bridge.available,
-        }
+        return service.health()
 
     @app.websocket("/ws")
     async def client_socket(websocket: WebSocket) -> None: