[产品讨论] PR #935 feat(mobile): expose composer attachment shortcuts

## 触发原因

PR #935 为手机端 composer 新增附件快捷入口，属于新增用户可见产品功能。

## 需要确认

- 该功能的交互设计是否经过产品讨论？
- 快捷入口的入口位置与触发方式是否符合产品规划？
- Desktop 端是否需要同步？

## 放行方式

产品白名单成员（@dashhuang / @xdanger / @MagicLizi / @zqchris）在本 issue 或 PR 评论区明确同意。

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关联 PR:#935(作者 @xSharkM);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,聊清楚后 PR 会恢复审查。

Start with PR #935 and this issue’s product questions about the mobile composer attachment shortcuts. Done requires explicit approval from a listed product whitelist member and a decision on the entry point, interaction, and whether Desktop should also change.

Written by the indexing model from the issue text.