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/configuration.md

@@ -0,0 +1,52 @@
+---
+sidebar_position: 4
+title: Configuration Reference
+description: All server.yaml configuration keys with defaults and matching environment variables.
+---
+
+# Configuration Reference
+
+BackupX loads `./config.yaml` from the working directory by default. You can override the path with `--config`. Every key can also be set via a `BACKUPX_` prefixed environment variable.
+
+## Full config reference
+
+```yaml title="config.yaml"
+server:
+  host: "0.0.0.0"             # BACKUPX_SERVER_HOST
+  port: 8340                  # BACKUPX_SERVER_PORT
+  mode: "release"             # release | debug
+
+database:
+  path: "./data/backupx.db"   # BACKUPX_DATABASE_PATH — embedded SQLite
+
+security:
+  jwt_secret: ""              # BACKUPX_SECURITY_JWT_SECRET — auto-generated if empty
+  jwt_expires_in: "24h"
+  encryption_key: ""          # AES-256-GCM key for storage config encryption
+
+backup:
+  temp_dir: "/tmp/backupx"    # BACKUPX_BACKUP_TEMP_DIR
+  max_concurrent: 2           # BACKUPX_BACKUP_MAX_CONCURRENT
+  retries: 3                  # Per-upload rclone low-level retries
+  bandwidth_limit: ""         # e.g. "10M" to cap transfers at 10 MB/s
+
+log:
+  level: "info"               # debug | info | warn | error
+  file: "./data/backupx.log"
+```
+
+## Secret generation
+
+If `jwt_secret` or `encryption_key` is empty on first start, BackupX generates a random value and persists it to the `system_configs` table. Keep a backup of `data/backupx.db` — losing it invalidates all existing encrypted storage configurations.
+
+## Environment variables
+
+The environment wins when both file and env are set. All dot-paths become underscores and uppercase:
+
+| Config key | Env variable |
+|------------|--------------|
+| `server.port` | `BACKUPX_SERVER_PORT` |
+| `log.level` | `BACKUPX_LOG_LEVEL` |
+| `backup.max_concurrent` | `BACKUPX_BACKUP_MAX_CONCURRENT` |
+| `backup.temp_dir` | `BACKUPX_BACKUP_TEMP_DIR` |
+| `backup.bandwidth_limit` | `BACKUPX_BACKUP_BANDWIDTH_LIMIT` |