docs: add Chinese TiDB Cloud CLI (tdc) Preview documentation

[Icemap]

变更内容

• 新增完整的 TiDB Cloud CLI（tdc）预览版中文文档，包括快速上手、核心概念、命令指南、场景示例和参考文档。
• 覆盖 TiDB Cloud Starter、TiDB Cloud 文件系统、FS Git、Journal、Vault、配置、安全、区域、安装和更新。
• 使用问题驱动的 Agent 场景，并说明 Git workspace 后台 hydration 的价值。
• 将全部页面加入 AI 文档导航。

变更原因

tdc 需要面向任务的产品文档，让新用户能够快速完成数据库或文件系统操作，同时完整说明命令面以及 tdc 与 Drive9 的职责边界。

用户影响

用户和 Coding Agent 可以按照受支持的 release 安装流程使用 tdc，理解凭证与平台边界，并将 tdc 应用于数据库、共享工作区、Git、Journal 和密钥委派场景。

验证

• PingCAP markdownlint
• Remark lint 和 PingCAP anchor 检查
• 内部与外部链接检查
• 当前 tdc 命令和参数覆盖检查
• 中英文命令块一致性检查

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[Icemap]

This is a translation PR, the original PR: pingcap/docs#23306