fix(frontend): increase api proxy timeout for long image generation

doc/html/nginx.conf

@@ -10,6 +10,9 @@ server {
         proxy_pass http://backend:8080/;
         proxy_http_version 1.1;
         proxy_request_buffering off;
+        proxy_connect_timeout 300s;
+        proxy_send_timeout 300s;
+        proxy_read_timeout 300s;
         proxy_set_header Host $host;
         proxy_set_header X-Real-IP $remote_addr;
         proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;