fix(ui): Remove extra background (#255)

Before

<img width="726" height="230" alt="CleanShot 2026-03-01 at 01 30 46@2x"
src="https://github.com/user-attachments/assets/904c409b-334f-4e3c-bdcb-53a94c713e13"
/>

After

<img width="726" height="240" alt="CleanShot 2026-03-01 at 01 30 19@2x"
src="https://github.com/user-attachments/assets/9f6a6b39-fdaa-4a34-baa0-6fc647bb74bf"
/>

Author: mufeez-amjad

ui/list.go

@@ -176,6 +176,7 @@ func (r *InstanceRenderer) Render(i *session.Instance, idx int, selected bool, h
 	remainingWidth := r.width
 	remainingWidth -= runewidth.StringWidth(prefix)
 	remainingWidth -= runewidth.StringWidth(branchIcon)
+	remainingWidth -= 2 // for the literal " " and "-" in the branchLine format string
 
 	diffWidth := runewidth.StringWidth(addedDiff) + runewidth.StringWidth(removedDiff)
 	if diffWidth > 0 {