fix(docker): update nginx configuration and simplify docker script (#903)

docker/docker-compose-dev.yaml

@@ -66,7 +66,7 @@ services:
     ports:
       - "2026:2026"
     volumes:
-      - ./nginx/${NGINX_CONF:-nginx.local.conf}:/etc/nginx/nginx.conf:ro
+      - ./nginx/${NGINX_CONF:-nginx.conf}:/etc/nginx/nginx.conf:ro
     depends_on:
       - frontend
       - gateway

docker/nginx/nginx.conf

@@ -30,10 +30,6 @@ http {
         server frontend:3000;
     }
 
-    upstream provisioner {
-        server provisioner:8002;
-    }
-
     # ── Main server (path-based routing) ─────────────────────────────────
     server {
         listen 2026 default_server;
@@ -189,8 +185,11 @@ http {
         }
 
         # ── Provisioner API (sandbox management) ────────────────────────
+        # Use a variable so nginx resolves provisioner at request time (not startup).
+        # This allows nginx to start even when provisioner container is not running.
         location /api/sandboxes {
-            proxy_pass http://provisioner;
+            set $provisioner_upstream provisioner:8002;
+            proxy_pass http://$provisioner_upstream;
             proxy_http_version 1.1;
             proxy_set_header Host $host;
             proxy_set_header X-Real-IP $remote_addr;