feat(frontend): add former name display, referral discount type, and refunds to bookings

Update frontend types, stores, and components to support name history display and new API fields.

- Add previousFirstName/previousLastName to User type and BookingUser type
- Add referral discount_source type and refunds array to Booking type
- Create nameDisplay.ts utility for rendering '(formerly ...)' labels
- Create booking.ts utility for booking-related helpers
- Update 25+ admin, payments, today, and account components to display
  former names on booking cards, modals, appointment views, and user lists

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

frontend/src/lib/components/admin/RescheduleModal.svelte

@@ -5,6 +5,7 @@
 	import { CalendarDate, getLocalTimeZone, type DateValue } from '@internationalized/date';
 	import { Checkbox } from '$lib/components/ui/checkbox';
 	import PolicyPopover from '$lib/components/ui/policyPopover.svelte';
+	import { formatUserName } from '$lib/utils/nameDisplay';
 
 	import * as Modal from '$lib/components/ui/dialog';
 	import { Button } from '$lib/components/ui/button';
@@ -495,7 +496,7 @@
 						})}
 					</div>
 					<div class="mt-1 text-sm text-gray-500">
-						{booking.user?.full_name || 'Unknown'} · {booking.services
+						{formatUserName(booking.user?.full_name || 'Unknown', booking.user?.previous_first_name, booking.user?.previous_last_name)} · {booking.services
 							?.map((s) => s.service_name)
 							.join(', ') || 'No services'} · {bookingDuration} min
 					</div>