Retrieve an itinerary grouped by guest

Retrieve the order's itinerary — the list of bookings on the order, grouped first by which guest they're for and then by date. Used by the operator-facing day-of-arrival view to print or display a per-guest schedule.

Each guest bucket lists the guest's name(s) plus one entry per date the guest has a booking on. Each date entry lists the bookings (name, start_time, end_time) sorted by start time.

Purchases (vouchers, products, memberships) are not included — only items that produce a scheduled booking.