chore(site): migrate scorecrux.com preview image to Chainguard nginx

site/Dockerfile

@@ -1,3 +1,20 @@
-FROM nginx:alpine
+# Static preview image for scorecrux.com.
+#
+# Chainguard nginx (rebuilt daily, zero known CVEs) per CLAUDE.md container policy.
+# Free-tier Chainguard is :latest-only, so this base cannot carry a digest pin.
+#
+# Two behavioural differences vs the previous nginx:alpine base:
+#   * it runs as non-root (uid 65532), so it cannot bind a privileged port;
+#   * its bundled conf.d/nginx.default.conf therefore listens on 8080, not 80.
+# The document root is unchanged (/usr/share/nginx/html), so the COPY below is
+# the same as before and no custom nginx config is needed.
+#
+# The base sets ENTRYPOINT ["/usr/sbin/nginx"] plus a CMD carrying the config
+# flags; both are deliberately left alone. The runtime has no shell, so anything
+# added here must be exec form.
+#
+#   docker build -t scorecrux-site site/
+#   docker run --rm -p 8888:8080 scorecrux-site   # was -p 8888:80
+FROM cgr.dev/chainguard/nginx:latest
 COPY index.html /usr/share/nginx/html/index.html
-EXPOSE 80
+EXPOSE 8080