[Feature] 支持在主会话中查看子代理的实时执行进度和重试继续子代理

[ViCrack]

Affected area

Desktop UI (agent-gui / React)

Problem statement (what should this solve)

当前通过 Agent 工具启动一个或多个子代理时，运行过程中缺少持续更新输出的执行信息。

卡半天不动不知道子代理在做什么，还有没有在跑

执行很久之后失败了，只能重新跑，而不能从断点续跑

Proposed behavior

希望每个子代理卡片在运行过程中能够实时点击查看输出，并且在出错的时候能够重试继续。

Estimated change scope

No response

Alternatives considered

No response

Pre-submit checklist

• I searched existing issues and pull requests and found no duplicates.
• This proposal is focused on a single feature or improvement.
• I understand a PR should come after this issue is confirmed by maintainers, otherwise it will be converted to draft.