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/Dockerfile

@@ -23,4 +23,8 @@ EXPOSE 8083
 HEALTHCHECK --interval=30s --timeout=3s --start-period=5s \
     CMD python -c "import urllib.request; urllib.request.urlopen('http://127.0.0.1:8083/health', timeout=2)"
 
-CMD ["uvicorn", "app.main:app", "--host", "0.0.0.0", "--port", "8083", "--proxy-headers", "--forwarded-allow-ips", "*"]
+# Transport limits as a last line of defence (the app enforces friendlier limits first):
+# messages are < 1 KB, so 64 KB is plenty; at most 1000 concurrent connections.
+CMD ["uvicorn", "app.main:app", "--host", "0.0.0.0", "--port", "8083", \
+     "--proxy-headers", "--forwarded-allow-ips", "*", \
+     "--ws-max-size", "65536", "--ws-max-queue", "16", "--limit-concurrency", "1000"]