feat: section-based service picker + per-appointment duration override (service mode)

Service-booking mode now selects services by section like slot mode:
appointment-booking-services returns service_section per item; ServiceSlotPicker
groups by section (SearchableSelect), accumulates picks across sections into a
removable 'section -> service' chip list.

Secretaries can override a service's duration for a single appointment without
changing the service default: appointment-service-slots accepts durations[uuid]
and both create endpoints accept service_durations; the override drives total
duration and slot_end. Online (patient) booking is unaffected — it never sends
overrides. Backend + frontend tests and docs updated.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

assets/admin/pages/AppointmentCreatePage.tsx

@@ -89,7 +89,7 @@ export default function AppointmentCreatePage() {
   // ── روش نوبت‌دهی پزشک (سرویسی/اسلاتی)
   const { bookingMode, services } = useDoctorBookingServices(doctorUuid);
   const serviceMode = bookingMode === 'service';
-  const [servicePick, setServicePick] = useState<{ serviceUuids: string[]; slot: { start: number; end: number } | null }>({ serviceUuids: [], slot: null });
+  const [servicePick, setServicePick] = useState<{ serviceUuids: string[]; durations: Record<string, number>; slot: { start: number; end: number } | null }>({ serviceUuids: [], durations: {}, slot: null });
 
   // ── زمان نوبت
   const [date, setDate] = useState(params.get('date') || today);
@@ -124,7 +124,7 @@ export default function AppointmentCreatePage() {
         patient_mobile: effectiveMobile,
         patient_national_code: effectiveNationalCode,
         ...(serviceMode
-          ? { service_item_uuids: servicePick.serviceUuids, duration_from_services: true }
+          ? { service_item_uuids: servicePick.serviceUuids, duration_from_services: true, service_durations: servicePick.durations }
           : {
               ...(sectionUuid ? { service_section_uuid: sectionUuid } : {}),
               ...(selectedServices.length ? { service_item_uuids: selectedServices.map(s => s.uuid) } : {}),