fix: add resolver for runtime DNS resolution in nginx

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Co-Authored-By: Claude <noreply@anthropic.com>

ai/nginx.conf.template

@@ -7,6 +7,10 @@ http {
     include /etc/nginx/mime.types;
     default_type application/octet-stream;
 
+    # DNS resolver for Tailscale MagicDNS
+    resolver 100.100.100.100 8.8.8.8 valid=30s;
+    resolver_timeout 5s;
+
     # Proxy settings
     proxy_http_version 1.1;
     proxy_buffering off;
@@ -34,7 +38,9 @@ http {
 
         location / {
             # Proxy to service on RunPod via Tailscale
-            proxy_pass http://${GPU_SERVICE_HOST}:${GPU_SERVICE_PORT};
+            # Use variable to force runtime DNS resolution (not startup)
+            set $backend http://${GPU_SERVICE_HOST}:${GPU_SERVICE_PORT};
+            proxy_pass $backend;
 
             # WebSocket upgrade
             proxy_http_version 1.1;