This PR fixes an issue where we'd show incorrect worktree labels when
opening a linked worktree directly. The linked worktree name would be
displayed in the project button but the dedicated worktree button would
be displaying "main", which is incorrect.

Now that we have a dedicated worktree button in the title bar, we can
make the project button always show the root repository name,
effectively matching the threads sidebar.

Release Notes:

- Fixed the title bar worktree button showing "main" when opening a
linked git worktree directly.