feat: add Docker support with Dockerfile, compose, CI, and oneliner install

- Multi-stage Dockerfile (node build + nginx:alpine serve)
- nginx.conf with SPA fallback, gzip, asset caching
- docker-compose.yml for easy deployment
- GitHub Actions workflow to build & push to ghcr.io on every push
- .dockerignore to keep image lean
- Updated README with Docker-first quick start and badge

.dockerignore

@@ -0,0 +1,7 @@
+node_modules
+dist
+.env
+.env.*
+!.env.example
+.git
+*.md