Issue #3610410: Adopt Orchestra's new human-task model in the example booking workflow and retire handler_url

Migrates the example booking workflow to Orchestra's new human-task model: the operator validation and refund-review steps become comment_task nodes, the deposit-hold-failed and attendance steps become plain user nodes, handler_url and action_title are dropped, and the bespoke order-review form and route are removed. The orders overview Workflow column reads the finder per-family act URL and label. Docs and the French translation are updated.

See #3610410.