feat(proxy): add per-IP rate and connection limits

The edge had no limit_req/limit_conn at all, so a single client could
flood the Next.js backend and the Nitro client with unbounded parallel
requests. Traefik's logs already showed this: bursts of gamedata icon
requests answered with 429.

Add limit_req (30r/s, burst 60, nodelay) and limit_conn (30) zones keyed
on the real client IP, applied at server scope so both cached assets and
proxied API routes share one budget. The burst is deliberately generous
because the Nitro client fetches gamedata and icons in bursts when
loading a room.

deployment/proxy/nginx.conf

@@ -44,6 +44,12 @@ http {
     client_header_buffer_size 1k;
     large_client_header_buffers 4 8k;
 
+    # Rate limiting per client IP. The Nitro client fetches gamedata and icons in
+    # bursts when booting a room, so the burst is deliberately generous: it caps
+    # sustained floods without punishing a normal room load.
+    limit_req_zone $binary_remote_addr zone=cms_req_per_ip:10m rate=30r/s;
+    limit_conn_zone $binary_remote_addr zone=cms_conn_per_ip:10m;
+
     # Blue/green cutover: ci-deploy.sh writes the active upstream here, and
     # `proxy_pass http://cms_app` below follows it via graceful nginx -s reload.
     upstream cms_app {