Should have keyboardy ways to select text and cut/copy/paste should all work in
the comment field. I think Charm has charm.land/x/clipboard for some of this,
and Crush uses a similar text field for their prompt field.
In the diff area, we should support copying a range after defining it, maybe with y since c is already used for create a comment. Or if that would be too awkward given keybinding conventions, maybe something else. I'm currently the only use so we can make whatever changes we need to be more intuitive and broadly familiar coming from other TUI apps.