Fix port-stripping redirect: use absolute_redirect off in nginx

Author: VargaJoe

nginx.conf

@@ -5,6 +5,11 @@ server {
     root /usr/share/nginx/html;
     index index.html;
 
+    # Use relative redirects so the original port (e.g. 9000 in local dev or a
+    # reverse-proxy port in production) is preserved instead of being replaced
+    # by nginx's internal port 80.
+    absolute_redirect off;
+
     # Serve pre-compressed .gz files generated by gatsby-plugin-zopfli
     gzip_static on;