Rename --docker-compose-hard-restart-required to --hard-compose-restart
and change its default from ["mailu"] to [] (nargs="*"): the compose
down/up is now opt-in, so compose hosts pass "mailu" while swarm hosts,
where the dir is a stack whose overlay network collides with compose up,
pass nothing. Make --backups-dir mandatory (no /var/lib/backup/ default)
so a run can never silently target the wrong backup root.
BREAKING CHANGE: the old flag name is removed, the implicit mailu default
is gone, and --backups-dir must be passed explicitly.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>