Add booking cancellation with a refund deadline

Adds a booking cancellation lifecycle to the Yoyaku example workflow.

A confirmed booking can always be cancelled up to the slot start; the resource refund_deadline policy decides only whether the cancellation is refunded.

• Resource refund_deadline (+ unit) field.
• Confirmation email carries a signed "Cancel booking" link + button; the link lands on a prefetch-safe confirmation screen (order summary + past-deadline notice).
• After confirmation the run forks into a cancellation branch and the deposit branch, rejoined by a quorum join: cancelling tears down the deposit branch (voiding any hold), cancels the order, runs an operator refund review only when a refund is due, and sends a dedicated cancelled notification.
• OrderNotifier carries the process variables in the event context (enables the orchestra_notification_template_suffix template override).

Kernel test for the schedule resolver + a functional cancel-path test; docs and French translations updated.