fix health check + build

Dockerfile

@@ -99,7 +99,9 @@ USER node
 WORKDIR /app/apps/frontend
 
 EXPOSE 5173
+# /healthz, not /: rendering / reaches the backend, so probing it would report
+# a backend outage as a dead frontend, and Traefik drops unhealthy containers.
 HEALTHCHECK --interval=30s --timeout=5s --start-period=20s --retries=3 \
-  CMD ["node", "-e", "fetch('http://127.0.0.1:'+(process.env.PORT||5173)+'/').then(r=>process.exit(r.ok?0:1)).catch(()=>process.exit(1))"]
+  CMD ["node", "-e", "fetch('http://127.0.0.1:'+(process.env.PORT||5173)+'/healthz').then(r=>process.exit(r.ok?0:1)).catch(()=>process.exit(1))"]
 
 CMD ["node", "server.js", "--prod"]