## Self-Review Checklist:

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

## Summary

Fixes an issue where the commit author avatar in the commit view could
be horizontally
compressed when editor gutter settings made the gutter unusually narrow.

The avatar column now keeps a minimum width based on the avatar size
plus horizontal
breathing room, while still using the editor gutter width when it is
larger. The spacing
scales with the UI rem size so the layout remains proportional under UI
scaling.

## Screenshots / Recording

- Before (default gutter)
<img width="686" height="336" alt="image"
src="https://github.com/user-attachments/assets/3474fd0b-fdfc-409d-a440-7bb54b28b42c"
/>

- Before (gutter disabled)
<img width="680" height="337" alt="image"
src="https://github.com/user-attachments/assets/66f873a2-1c98-4029-a65c-687171d2aebd"
/>

- After (default gutter)
<img width="687" height="532" alt="image"
src="https://github.com/user-attachments/assets/94ea04e2-644c-491f-8f70-9353af7003d8"
/>

- After (min_line_number_digits: 1)
<img width="685" height="535" alt="image"
src="https://github.com/user-attachments/assets/7080409c-dfa6-4ea6-8255-6de2a59f87fa"
/>

- After (gutter disabled)
<img width="683" height="529" alt="image"
src="https://github.com/user-attachments/assets/e3a5ec33-36a0-4581-8421-2676df59c859"
/>


## Testing

  - Ran `cargo check -p git_ui`

## Release Notes:

- Fixed commit author avatars being compressed in the commit view when
editor gutters are narrow.