Lobby: WebSockets for real-time sync

Server pushes small change notes (messages / lobby / sheet) per lobby;
clients fetch data through the normal API so visibility rules stay in one
place. Polling stays as slow fallback. nginx WebSocket headers documented.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HJhXuLD2Z6hv3Wqeq9UL9K

DEPLOY.md

@@ -70,10 +70,17 @@ server {
         proxy_set_header X-Forwarded-For $remote_addr;   # overwrite, so clients cannot fake their address
         proxy_set_header X-Forwarded-Proto $scheme;
         proxy_set_header X-Forwarded-Host $host;
+        # the lobby uses a WebSocket for live updates (without these three lines it falls back to polling)
+        proxy_http_version 1.1;
+        proxy_set_header Upgrade $http_upgrade;
+        proxy_set_header Connection "upgrade";
+        proxy_read_timeout 3600s;
     }
 }
 ```
 
+Already running an older config? Add the last four lines inside `location /`, then `sudo nginx -t && sudo systemctl reload nginx`. Nothing else changes; the lobby still works without them, just with a few seconds of delay.
+
 ```bash
 sudo ln -s /etc/nginx/sites-available/aw /etc/nginx/sites-enabled/aw
 sudo nginx -t && sudo systemctl reload nginx