build(docker): add Docker build and deployment infrastructure

- Add multi-stage Dockerfile with pnpm install and Nginx serving
- Add nginx.conf with gzip and SPA fallback
- Add docker-build.sh script for building and pushing images
- Add .dockerignore for build context optimization
- Remove unused pnpm-workspace.yaml

nginx.conf

@@ -0,0 +1,21 @@
+server {
+    listen       80;
+    server_name  _;
+    root         /usr/share/nginx/html;
+
+    gzip on;
+    gzip_types text/css application/javascript application/json image/svg+xml;
+    gzip_vary on;
+
+    # SPA fallback
+    location / {
+        try_files $uri /index.html;
+    }
+
+    # 可选的 API 代理，取消注释并改 backend 地址即可
+    # location /api/ {
+    #     proxy_pass http://backend:8080;
+    #     proxy_set_header Host $host;
+    #     proxy_set_header X-Real-IP $remote_addr;
+    # }
+}