fix(infra) : update proxy port to 8086 and add maintenance mode

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

infra/prod/nginx-proxy.conf

@@ -21,7 +21,7 @@ server {
     }
 
     location / {
-        proxy_pass http://127.0.0.1:8083;
+        proxy_pass http://127.0.0.1:8086;
         proxy_set_header Host $host;
         proxy_set_header X-Real-IP $remote_addr;
         proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;