Add git worktree status-line item (implementation complete on fork)

What variant of Codex are you using?

CLI

What feature would you like to see?

A configurable TUI status-line item named git-worktree that displays the current Git checkout’s worktree root directory name.

The item should be opt-in only and wouldn't change the default status line. When enabled, it renders only in the TUI status line, not in the terminal title. It should resolve the active status-line cwd to its Git repository/worktree root, display only that root directory’s basename, and silently omit itself when the cwd is not inside a Git checkout.

Additional information

The implementation is complete and can be viewed as an open pull requests on my fork: https://github.com/americanhanko/codex/pull/1

I suspect the change is trivial enough that I can be granted temporary contributor permissions to get it merged.