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

nginx.conf

@@ -0,0 +1,21 @@
+server {
+    listen 80;
+    server_name _;
+    root /usr/share/nginx/html;
+    index index.html;
+
+    location / {
+        try_files $uri $uri/ /index.html;
+    }
+
+    # Cache static assets
+    location /assets/ {
+        expires 1y;
+        add_header Cache-Control "public, immutable";
+    }
+
+    # Gzip
+    gzip on;
+    gzip_types text/plain text/css application/json application/javascript text/xml application/xml text/javascript image/svg+xml;
+    gzip_min_length 256;
+}