product 签字: #1183 fix(desktop): allow collapsing the file browser tree

## 触发

`product`: 在文件浏览器树中新增折叠/展开交互能力，涉及新 hook、i18n 键和 UI 状态管理。

## PR

https://github.com/makecindy/cindy/pull/1183

## 放行方式

roster 任一成员直接在 PR 上 GitHub Approve 即放行。需要修改请 Request Changes，作者改完后重新 Approve。

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关联 PR:#1183(作者 @yuaiccc);本 issue 由 review-pr 流程自动创建,用于先讨论该 PR 涉及的产品 / UI 变更,维护者确认后 PR 会恢复推进。

Start with linked PR #1183 and review its proposed file-browser tree changes, including the new hook, i18n key, and UI state management. Done means the product/UI change is confirmed by a roster member's GitHub approval, or requested changes have been addressed and approved.

Written by the indexing model from the issue text.