1.4.0 — get_checkout_status

Fifth tool: get_checkout_status. create_checkout_link now returns a session_id
and puts it in the handoff link; the new tool reports whether the human opened
checkout, paid, and whether the label exists, with the tracking number once it
does. DHL Express named where it rates (Germany, Australia). Sessions live 30
days; the answer never carries names, addresses or emails.