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/sessions.py

@@ -24,6 +24,8 @@ logger = logging.getLogger(__name__)
 class Connection:
     def __init__(self, websocket: WebSocket) -> None:
         self.websocket = websocket
+        # Client IP; behind the reverse proxy uvicorn takes it from X-Forwarded-For.
+        self.ip = websocket.client.host if websocket.client else "unknown"
         self._queue: asyncio.Queue[dict[str, Any] | None] = asyncio.Queue()
         self._writer: asyncio.Task | None = None
 
@@ -85,6 +87,9 @@ class SessionRegistry:
     def remove(self, session: Session) -> None:
         self._by_token.pop(session.token, None)
 
+    def connected(self) -> list[Session]:
+        return [s for s in self._by_token.values() if s.connected]
+
     def expired(self, ttl: float) -> list[Session]:
         now = time.monotonic()
         return [s for s in self._by_token.values() if not s.connected and now - s.last_seen > ttl]