fix: add stub hosts for nginx upstream resolution in CI

Author: rmdes

.github/workflows/validate.yml

@@ -22,7 +22,13 @@ jobs:
         run: docker compose config --quiet
 
       - name: Check nginx config syntax
-        run: docker run --rm -v "$PWD/nginx.conf:/etc/nginx/nginx.conf:ro" nginx:alpine nginx -t
+        run: |
+          # Add stub DNS entries for upstream hosts so nginx -t doesn't fail on DNS
+          docker run --rm \
+            -v "$PWD/nginx.conf:/etc/nginx/nginx.conf:ro" \
+            --add-host app:127.0.0.1 \
+            --add-host bot:127.0.0.1 \
+            nginx:alpine nginx -t
 
       - name: Verify GHCR image exists
         run: |