Release v4.187.2

Fixed

• A command form (add to basket, the checkout wizard) in a Stage served under a path prefix, such as Studio's Play at /api/play/{id}/, posted to the root of the host and was refused with 405: the form is Arc's own CommandForm, which builds its command from Arc's default configuration, whose base path is empty, so the earlier fix in the command executor (#634) never reached it. The form now points its command at the path the page is served under before it executes (#618).