Create a reservation (staff side)

Writes a whole period at once: "the period called `name` now runs on exactly these days, with these settings". No active period for a weekday means an empty availability grid that day, so this is the endpoint a venue's bookable times live or die by. **PUT, and wholesale, on purpose.** A day of a period is not an entity an operator names; the PERIOD is, and it is identified by its `name`. There is nothing here for a per-row create to be idempotent about, and the old `POST` (one weekday per call) is what made a restaurant serving lunch and dinner all week fourteen separate writes. **One statement, therefore one transaction.** The whole replacement happens inside `book_replace_service_period_group()` (migration 0029) rather than as a PostgREST delete followed by an insert. That is not tidiness: `computeReservationSlots` returns nothing for a day with no periods, so a delete that landed without its insert would take the venue's booking page **offline** until someone re-saved, not merely degrade it. On any error nothing is written and nothing is lost. Gated to admin, or a staff login granted `manage_services` (migration 0082), hospitality's equivalent of the appointments services routes, and gated the same way: an empty `days` array deletes the group, so this one call is as destructive as it is creative.