fix: add explicit USER 101 to prod stage Dockerfile

Kubernetes runAsNonRoot validation requires the USER directive to be
explicitly set in the image metadata. nginx-unprivileged runs as UID 101
internally, but without the explicit USER directive Kubernetes cannot
verify this from the image config and fails with CreateContainerConfigError.

Fixes CAR-231.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

Dockerfile

@@ -9,13 +9,14 @@ RUN npm ci
 COPY . .
 RUN npm run build
 
-# Stage 2: Production
-FROM nginx:stable-alpine AS prod
+# Stage 2: Production — uses nginxinc/nginx-unprivileged which runs as non-root (UID 101)
+FROM nginxinc/nginx-unprivileged:stable-alpine AS prod
 
 COPY --from=build /app/dist /usr/share/nginx/html
 COPY nginx.conf /etc/nginx/conf.d/default.conf
 
-EXPOSE 80
+USER 101
+EXPOSE 8080
 
 HEALTHCHECK --interval=30s --timeout=3s --start-period=5s --retries=3 \
-  CMD wget -qO- http://localhost/health || exit 1
+  CMD wget -qO- http://localhost:8080/health || exit 1

nginx.conf

@@ -1,5 +1,5 @@
 server {
-    listen 80;
+    listen 8080;
     server_name _;
     root /usr/share/nginx/html;
     index index.html;