Self-Review Checklist:

- [x] I've reviewed my own diff for quality, security, and reliability
- [x] Unsafe blocks (if any) have justifying comments
- [x] The content is consistent with the [UI/UX
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
- [x] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable

Summary:

- Added a toggleable tree view for changed files in the git graph commit
details panel
- Reused shared ListItem rows and file icon folder rendering for
changed-file entries
- Kept flat view available for status-sorted changed files

Tests:

- cargo check -p git_graph

Release Notes:

- Improved commit details changed-file lists with an optional tree view