[Desktop] Subagent UI 不可见 - 建议添加子任务展示界面

[lapwno]

现状

Desktop 版对话界面没有子 agent 和主 agent 的划分，用户无法看到哪些是子任务在后台运行，也无法了解每个子任务的 token 消耗。

建议

参考 TUI 侧边栏的子任务树状界面，在 Desktop 版中增加：

1. 对话中显示哪些是子任务
2. 每个子任务的 token 和费用耗
3. 支持展开/折叠子任务详情

参考

TUI 已有此功能（PR #25712 + Issue #11027），建议 Desktop 对接相同的 API

[github-actions]

This issue doesn't fully meet our contributing guidelines.

What needs to be fixed:

• This appears to be a feature request, but the title does not start with [FEATURE]: as required by the feature request template.
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Please edit this issue to address the above within 2 hours, or it will be automatically closed.

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This issue might be a duplicate of existing issues. Please check:

• [FEATURE]: Live session status panel in sidebar + background session completion notifications #28175: Requests a live session status panel showing background/subagent session status — very similar goal of surfacing subagent visibility in the UI
• [FEATURE]: Add Run/Debug button + visualize background processes in Desktop, support multi-config & process management #18708: Requests visualization of background processes started by subagents in Desktop — overlaps with the subagent UI visibility request here

If you believe this was flagged incorrectly, please let a maintainer know.

[github-actions]

This issue has been automatically closed because it was not updated to meet our contributing guidelines within the 2-hour window.

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