Embed (automatic) cleanup options to remove old sessions

### Feature summary

Cleanup old worktrees and storage

### What problem are you trying to solve?

My machine was running out of storage and I suspected that worktrees of my AI tools could be a part of the issue. So I checked the `.copilot` folder and indeed: 200 GB of storage used!!!

### Proposed solution

Enable proper data cleanup on old sessions, especially the ones that where completed with a merged pr, as those are the most likely to never be needed.

### Workflow impact

Make my machine usable again!

### Installation context

_No response_

### Additional context

Claude Code handles this perfectly for me with this (just discovered) setting:

未指定任何文件、测试或入口点。首先定位会话、worktree 和 .copilot 存储的管理位置，然后为旧会话定义清理行为，尤其是与已合并 pull requests 相关的会话。完成后应包含一个可用的清理选项，以防止旧 worktree 和会话数据消耗过多存储空间。

由索引模型根据 Issue 内容生成。