The worktrees tab now displays the checked-out branch (or detached HEAD
state) for each worktree, making it much easier to see which worktree
holds which branch.
This is useful when you need to "unlock" a branch that's occupied by
another worktree: you can now clearly see which worktrees are on a
branch vs detached, without having to select each one individually.
Also rename the "(main)" label to "(main worktree)" to avoid confusion
with the common "main" branch name, and move it after the branch column.
