Appointments could only reference a single service (ManyToOne). Add an
appointment_service_items join table (ManyToMany) so an appointment can
carry several services; the first stays the primary service_item for
backward compatibility, and toArray now also returns service_items[].
Both create endpoints (my/appointment, admin/appointment) accept
service_item_uuids[] and attach all of them. A new duration_from_services
flag gates the slot_end recompute: service-booking mode sends it true
(slot_end = start + Σ durations); slot mode omits it so the manual end
time is preserved. The admin endpoint previously ignored services entirely.
Frontend: in slot mode the single service dropdown becomes a checkbox list
filtered by the selected section (multi-select); service mode sends the
duration flag. Migration + backend/entity tests + docs updated.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
