A refused rate change on the place map is silently ignored

Every seat in the picker's basket panel carries a rate dropdown. Changing it posts op: category to the place-op endpoint, and the endpoint can refuse: when the place is no longer held it answers 409 with {ok: false, error: 'Not held.'}, which happens if the hold lapsed while the panel sat open.

The picker ignores the refusal. The change handler re-renders and updates the seat's rate only inside its success branch, and there is no else and no catch, so on a refusal nothing at all happens: the dropdown keeps showing the rate the server rejected, while the total, which is only recomputed by that same re-render, goes on showing the old one. The panel ends up contradicting itself, and a network error is a silent unhandled rejection.

What makes it stand out is that the neighboring refusals are all handled. A seat someone else has taken turns unavailable and is announced. A pooled area that cannot give another unit corrects its counter and says why. Only the rate dropdown fails silently.

The fix is small, because re-rendering the panel restores the dropdown from the rate the seat is actually held at. On a refusal, re-render (which reverts the control) and announce it, matching what the seat and pool paths already do. A catch should do the same with a generic message.

Found while adding browser coverage in #3614039: Add FunctionalJavascript coverage for the place map and calendar JavaScript. The test there covers changing a rate successfully and notes in a comment that the refusal path is deliberately not asserted, because it was this bug rather than behavior worth pinning; that test should be extended once this is fixed.