Deleting a worktree leaves the branch in the source repo

### Short summary

Files aren't fully cleaned up when deleting wortrees

### Affected version or release

0.2.2

### Installation context

darwin arm64

### What happened?

Deleting a session doesn't fully clean up the files

### Steps to reproduce

If you follow these steps:
- Open a local project
- Start a new session / do some stuff
- Delete it (and click the confirm button that the files associated to it will be deleted)

You are still left with a branch in the source repository.

### Expected behavior

Feels like that should be removed too when you delete the session?

### Additional context

_No response_

Start by reproducing the session deletion workflow on darwin arm64 and trace where the app removes the worktree and associated files. Confirm the cleanup path for the source repository; done means deleting a session also removes its branch from that repository.

由索引模型根据 Issue 内容生成。