sidebar: Show branch name after worktree name (#53900)

<img width="297" height="505" alt="Screenshot 2026-04-14 at 3 20 23 PM"
src="https://github.com/user-attachments/assets/90366ccd-86db-497e-9c81-af94b4144ebe"
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Display the git branch name alongside the worktree name in the sidebar's
thread list (or without the worktree name, if it's a main worktree).

Release Notes:

- Added branch name display next to worktree names in the agent sidebar
thread list.
dc5e2f1c24Richard Feldman committed on 4/15/2026, 4:42:28 AM· committed by GitHubparent6beecae
6 files changedLine totals unavailable