fix(api): use server.listen instead of app.listen for WebSocket support

- server.ts: switch from app.listen() to server.listen() so WebSocket
  upgrade handler is on the same server as HTTP requests
- lobbyService: add host as first player on lobby creation
- ws-client: guard against reconnect when already connecting
- ws-provider: skip connect if already connected

apps/web/src/lib/ws-provider.tsx

@@ -9,6 +9,8 @@ export const WsProvider = ({ children }: { children: ReactNode }) => {
   const [isConnected, setIsConnected] = useState(false);
 
   const connect = useCallback(async (url: string): Promise<void> => {
+    if (wsClient.isConnected()) return;
+
     wsClient.onClose = () => setIsConnected(false);
     wsClient.onError = () => setIsConnected(false);
     try {