feat(frontend): integrate custom services across booking flow and routes

Update BookingFlow to support custom service selection, add custom_services to booking types, and link CustomServicesManagement into admin pages. Minor updates to schedules, prices, and today routes.

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

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

frontend/src/lib/components/today/TodayCalendar.svelte

@@ -744,7 +744,7 @@
 										{item.data.user_name}
 									</button>
 									<div class="flex flex-wrap items-center gap-x-1 text-sm text-gray-600">
-										<span class="truncate">{item.data.services.join(', ')}</span>
+										<span class="truncate">{(item.data.services ?? []).join(', ')}</span>
 										<span
 											class="shrink-0 rounded-full bg-gray-100 px-1.5 py-0.5 text-xs font-medium"
 										>