CCR is not triggered when assigned to Copilot from PR

### Short summary

CCR is not triggered when assigned to Copilot from PR

### Affected version or release

v1.0.19

### Installation context

Just normal install

### What happened?

1. Create a session and do something to make code changes in a worktree
2. Open a PR
3. Assign Copilot as a "Reviewer"
4. CCR should be triggered, but it is not, i have to go to the website to request

ALSO, if you assign copilot as an assignee it will trigger a new cloud agent session, which is weird

### Steps to reproduce

_No response_

### Expected behavior

_No response_

### Additional context

_No response_

复现 issue 中的工作流：创建一个包含 worktree 更改的 session，打开一个 PR，并将 Copilot 指定为 reviewer 而不是 assignee。将该行为与直接指定 Copilot 以及从网站发起请求进行比较；完成的标准是，指定为 reviewer 会触发 CCR，且不会启动意外的 cloud agent session。

由索引模型根据 Issue 内容生成。