git_panel: Add some UI improvements (#54630)

Nothing major, just some small quality of life improvements here:

- Makes the header's checkmark always visible and the entire row surface
area a clickable target
- Only displays the project picker when there is more than one repo;
this avoids having to show a disabled button

Release Notes:

- N/A
a00f07381cDanilo Leal committed on 4/23/2026, 3:12:45 PM· committed by GitHubparent3eb0bab
1 file changedLine totals unavailable