文档: 新增 Docusaurus 官网与双语文档，README 切换为英文默认 (#39)

- 新建 docs-site/ Docusaurus 项目，支持 en + zh-Hans 双语
- 从 README 迁移内容为独立文档页面：
  - Getting Started（安装、快速开始）
  - Deployment（Docker、裸机、Nginx、配置参考）
  - Features（备份类型、存储后端、SAP HANA、多节点集群、通知）
  - Reference（API、CLI）
  - Development（开发、贡献）
- 自定义 BackupX 主题色、logo、落地页组件
- 新增 .github/workflows/docs.yml，Actions 自动构建并发布到 GitHub Pages
- README.md 切换为英文，中文版挪到 README.zh-CN.md，两者均精简为导航型
- 配置站点 URL：https://awuqing.github.io/BackupX/

docs-site/docs/deployment/nginx.md

@@ -0,0 +1,53 @@
+---
+sidebar_position: 3
+title: Nginx Reverse Proxy
+description: Expose BackupX behind Nginx with HTTPS and SSE-friendly buffering disabled.
+---
+
+# Nginx Reverse Proxy
+
+A minimal production-ready Nginx site for BackupX:
+
+```nginx title="/etc/nginx/sites-available/backupx"
+server {
+    listen 80;
+    server_name backup.example.com;
+
+    # Static UI (served from /opt/backupx/web)
+    location / {
+        root /opt/backupx/web;
+        try_files $uri $uri/ /index.html;
+    }
+
+    # API reverse proxy
+    location /api/ {
+        proxy_pass http://127.0.0.1:8340;
+        proxy_http_version 1.1;
+        proxy_set_header Host $host;
+        proxy_set_header X-Real-IP $remote_addr;
+        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+        proxy_set_header X-Forwarded-Proto $scheme;
+
+        # Large uploads (restore flow)
+        client_max_body_size 0;
+
+        # Live log stream uses SSE — buffering must be off
+        proxy_buffering off;
+        proxy_read_timeout 3600s;
+        proxy_send_timeout 3600s;
+    }
+}
+```
+
+## HTTPS with certbot
+
+```bash
+sudo apt install certbot python3-certbot-nginx
+sudo certbot --nginx -d backup.example.com
+```
+
+Certbot rewrites the config to listen on 443 with auto-renewal.
+
+:::caution Agent needs a stable URL
+If Master is behind HTTPS, remote Agent deployments must use the public HTTPS URL for `--master`. Self-signed certs require `--insecure-tls` (testing only).
+:::