Self-Review Checklist:

- [x] I've reviewed my own diff for quality, security, and reliability
- [ ] 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)
- [ ] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable

Hello Zed Team, this is my first contribution. I use Zed every day and
have always wanted to see the total for the plus/minus counts in the Git
diff panel. Here is my attempt to make that happen. Please let me know
if there are any issues and I will fix them. Thank you.

Adds git diff stats to the Git panel so users can see the total number
of added and removed lines while reviewing changes.

Verified locally by compiling and running Zed, then confirming the Git
panel displays the diff count as expected.

Release Notes:

- Improved Git panel diff visibility by showing total added and removed
line counts.

<img width="1540" height="1098" alt="zed-add-git-diff-plus-minus-count"
src="https://github.com/user-attachments/assets/5051944e-7cf5-4bb0-81d3-10228e619690"
/>