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_website/src/App.tsx

@@ -10,10 +10,12 @@ const STATUS_MESSAGES = {
   connecting: 'Connecting to the server…',
   closed: 'Connection lost. Reconnecting…',
   replaced: 'This game was opened in another window. Reload the page to continue here.',
+  busy: 'The server is full right now. Retrying in a moment…',
 } as const
 
 function App() {
-  const { status, playerId, lobby, game, completedTrick, toasts, dismissToast, actions } = useWizard()
+  const { status, playerId, lobby, game, completedTrick, serverStatus, toasts, dismissToast, actions } =
+    useWizard()
   const lobbyCode = lobby?.code
 
   // Keep the lobby code in the address bar so the URL can be shared as an invite link.
@@ -27,9 +29,22 @@ function App() {
 
   let screen
   if (!lobby || !playerId) {
-    screen = <HomeScreen connected={status === 'open'} actions={actions} />
+    screen = (
+      <HomeScreen
+        connected={status === 'open'}
+        acceptingGames={serverStatus.accepting_games}
+        actions={actions}
+      />
+    )
   } else if (lobby.status === 'waiting' || !game) {
-    screen = <LobbyScreen lobby={lobby} playerId={playerId} actions={actions} />
+    screen = (
+      <LobbyScreen
+        lobby={lobby}
+        playerId={playerId}
+        acceptingGames={serverStatus.accepting_games}
+        actions={actions}
+      />
+    )
   } else {
     screen = (
       <GameScreen