Offer cards print their price in different places when one of them has a selling limit

On the slot booking page a selling limit is set as the quantity field's own description. A theme renders a field description inside the field's own column, and the sentence is wider than the minus/value/plus stepper it belongs to, so the column holding the stepper grows by the difference. The price sits next to that column and moves with it: an offer carrying a limit prints its price about 35 pixels left of every offer without one, and the price is the one thing two offers are compared by.

The form item's own field-stack margin adds to it. The card is a line taller than its neighbours, and the price is centered against the whole column rather than against the stepper, so it no longer sits on the stepper's line either.

Steps to reproduce: attach the per-order quantity limit policy to a resource that sells several tariffs, then open a session's booking page. The card carrying the limit prints its price left of the others.

Proposed resolution: carry the sentence as a card variable rather than as the field's description, and let the card place it on its own line under the price and the control, which become one group ending where every other card's group ends. The field points at that line with aria-describedby, which core wired for it while the sentence was a description, so someone reaching the control by keyboard still hears why the plus button stops.

Two cascade defects found in the same place: the button at the ceiling is marked aria-disabled rather than disabled on purpose, so that a keyboard user pressing plus up to the maximum is not dropped to the top of the page, but the module's rule for it is exactly as specific as a theme's own rule for a button and loads earlier, so the spent button kept a pointer cursor. The rule zeroing the form item's margin lost the same tie against system/form.css.