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/EditBookingModal.svelte

@@ -3,6 +3,7 @@
 	import { SvelteDate } from 'svelte/reactivity';
 	import { toast } from 'svelte-sonner';
 	import { formatDuration } from '$lib/utils/format';
+	import { formatUserName } from '$lib/utils/nameDisplay';
 	import * as Modal from '$lib/components/ui/dialog';
 	import * as AlertDialog from '$lib/components/ui/alert-dialog';
 	import { Button } from '$lib/components/ui/button';
@@ -95,7 +96,9 @@
 								referral_code: data.user.referral_code,
 								referral_code_uses: data.user.referral_code_uses,
 								created_at: data.user.created_at,
-								notes: data.user.notes
+								notes: data.user.notes,
+								previous_first_name: data.user.previous_first_name,
+								previous_last_name: data.user.previous_last_name
 							}
 						: undefined,
 					services: (data.services || []).map((s: BookingService) => ({
@@ -418,7 +421,7 @@
 					<div class="grid gap-3 md:grid-cols-2">
 						<div>
 							<div class="text-xs text-gray-500">Name</div>
-							<div class="font-medium">{booking.user?.full_name || '—'}</div>
+							<div class="font-medium">{formatUserName(booking.user?.full_name || '—', booking.user?.previous_first_name, booking.user?.previous_last_name)}</div>
 						</div>
 						<div>
 							<div class="text-xs text-gray-500">Email</div>