Clean up internal doc

_↴ Ported from [flutter/genui#456](https://github.com/flutter/genui/issues/456) — originally opened by [sethladd](https://github.com/sethladd) on 2025-10-27._
_Original labels: P2, sla: missed_

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Teams inside of Google are finding our internal docs, some of which are outdated. Let's clean those up so those teams have an accurate picture.

For example, this one: /mobile/flutter/genui/g3doc/index.md

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### 1 comment(s) from the original issue

**[sethladd](https://github.com/sethladd)** commented on 2025-10-28:

I put up a CL for this, with a warning that the doc is out of date. We can do more here, so I'll leave the issue open

找到内部文档文件 /mobile/flutter/genui/g3doc/index.md。检查其内容以识别过时的信息。更新或删除过时的部分，确保文档准确反映项目的当前状态。检查是否还有类似的内部文档也需要清理。

由索引模型根据 Issue 内容生成。