Build a parent parser whose -h invokes help_fn.
This eliminates boilerplate: without the helper every add_parser
call would need its own three-line parent-parser setup. Used by both
main.parse_args and skills.commands.setup_skills_parser.
Zero-argument callable that renders a Rich help screen.
Factory that turns help_fn into an argparse
Action class (see main._make_help_action).
