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

Dockerfile

@@ -0,0 +1,14 @@
+# Stage 1: Build
+FROM node:22-alpine AS build
+WORKDIR /app
+COPY package.json package-lock.json ./
+RUN npm ci
+COPY . .
+RUN npm run build
+
+# Stage 2: Serve
+FROM nginx:alpine
+COPY --from=build /app/dist /usr/share/nginx/html
+COPY nginx.conf /etc/nginx/conf.d/default.conf
+EXPOSE 80
+CMD ["nginx", "-g", "daemon off;"]