维护者确认 · #2942 feat(browser): sandboxed local HTML preview

## 确认类别

product

## 触发原因

新增沙箱化本地 HTML 预览能力（tokenized 访问），涉及安全和架构。

## 需要维护者确认

新增本地文件预览服务器，涉及 security 和 arch 触发，需确认方向。

## 如何放行

在 PR 上 Approve 即可；如需作者修改请 Request Changes。

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关联 PR:#2942(作者 @happy9zhang);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 by reading PR #2942 and its sandboxed local HTML preview design, especially the tokenized access, security, and architecture considerations described here. Done means a maintainer decides whether the product and UI change is acceptable by approving the PR or requesting changes.

Written by the indexing model from the issue text.