Switch from server-side builds to pre-built images:
- Add build-and-push.sh for local builds to GHCR
- Update deploy.sh to pull from registry (30s vs 20min)
- Add docker-compose.build.yml for local build fallback
- Update docker-compose.yml to use registry image
- Add GHCR_USER/GHCR_TOKEN to env.example
- Add npm scripts: docker:build, docker:deploy, docker:backup
