Say the booking is confirmed once, not twice

Problem/Motivation

The booking confirmation page tells the booker "Your booking is confirmed." twice, with the booking list between the two.

n_confirm carries stacking keep, so its confirmation and the bookings list stay on the page as the process moves on. n_await_guarantee, the wait node it forks into, then announces the same sentence again.

Proposed resolution

Remove the interaction from n_await_guarantee. It waits for the guarantee window and asks the booker for nothing, and the confirmation it was repeating is already on the page and carries the booking list as well. n_cancel_window, the other branch of the same fork, already has no message of its own.

Remaining tasks

None. A site that already has the workflow installed needs its active config migrated and a new workflow version published, since config/install only reaches a fresh install and running instances execute a pinned snapshot.

User interface changes

The confirmation page says the booking is confirmed once.

API changes

None.

Data model changes

None.

AI-Generated: Yes (Claude Code was used to help draft this issue summary and to write the code on the merge request. I reviewed and ran the work myself before posting it.)