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/intro.md

@@ -0,0 +1,40 @@
+---
+id: intro
+slug: /intro
+sidebar_position: 1
+title: Introduction
+description: Overview of BackupX — a self-hosted server backup management platform.
+---
+
+# BackupX
+
+**BackupX** is a self-hosted server backup management platform. One static binary, one command, and every backup job for every server is under control.
+
+- **Single binary + embedded SQLite** — no external database or orchestrator required
+- **Files, databases, SAP HANA** — in one place, with a visual scheduler
+- **70+ storage backends** — Alibaba OSS, Tencent COS, Qiniu, S3, Google Drive, WebDAV, FTP, plus SFTP / Azure Blob / Dropbox / OneDrive and dozens more via rclone
+- **Multi-node cluster** — Master-Agent mode manages backups across servers, agents run tasks locally and upload straight to storage
+- **Secure by default** — JWT auth, bcrypt, AES-256-GCM encrypted config, optional backup encryption, full audit log
+
+## Architecture at a Glance
+
+```
+[Web Console] ─── JWT ──→ [Master (backupx)]
+                             │
+                             │ HTTP long-poll (token auth)
+                             ▼
+                         [Agent (backupx agent)]
+                             │
+                             ▼
+                     [70+ Storage Backends]
+```
+
+Tasks routed to the local Master run in-process; tasks assigned to remote nodes are dispatched through a command queue and executed by the Agent locally. Agents only ever initiate outbound HTTP — no reverse connectivity required.
+
+## Where to Next
+
+- **New to BackupX?** Read the [Quick Start](/docs/getting-started/quick-start) first.
+- **Deploying to production?** See the [Deployment Guide](/docs/deployment/docker).
+- **SAP HANA operator?** Both `hdbsql` Runner and native Backint are supported — see [SAP HANA](/docs/features/sap-hana).
+- **Managing multiple servers?** See [Multi-Node Cluster](/docs/features/multi-node).
+- **Integrating programmatically?** See the [API Reference](/docs/reference/api).