Docker Hub unreachable from k3s cluster. Switch Dockerfile to pull
node and nginx base images from Harbor registry.
Co-Authored-By: Claude <noreply@anthropic.com>
Multi-stage Docker build: node:20-alpine + nginx:1.27-alpine.
CI builds and pushes to harbor-in-k3s.cheverjohn.me/iloom/iloom-frontend.
Co-Authored-By: Claude <noreply@anthropic.com>