[Suggestion]: Add Collapse Feature for Left-Side Menu

首先定位 React 文档网站左侧导航的实现，并查看 Hooks 和 Components 等部分是如何渲染的。确定当前已打开部分的折叠和展开应如何表现，然后验证用户无需进行大量滚动即可访问其他部分。该 issue 未指出任何文件或测试，因此必须先找到相关入口点。

Summary

The left-side navigation menu in the React official documentation currently lacks a collapse feature. When navigating through long lists, users have to scroll to the bottom to access other sections. This can be inconvenient, especially when switching between categories such as “Hook” or “Components”.

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Details

Proposal:
Add a collapse/expand functionality for the left-side navigation menu. This would allow users to collapse currently opened sections and easily navigate to other sections without extensive scrolling.

Additional Information:
I would be happy to contribute to this feature and submit a pull request to implement the collapse functionality. Please let me know if this is something the team is open to, and I can start working on it.

Thank you for considering this feature request!