Add a friendly 502/503/504 page (nginx serves it directly, no backend needed)

nginx-labelprint.conf

@@ -17,4 +17,10 @@ server {
         proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
         proxy_set_header X-Forwarded-Proto $scheme;
     }
+
+    error_page 502 503 504 /502.html;
+    location = /502.html {
+        root /etc/nginx/error_pages;
+        internal;
+    }
 }