feat: refactor onboarding into a multi-step flow with dedicated routes and session state management

apps/frontend/src/routes/onboard/complete.tsx

@@ -0,0 +1,6 @@
+import { OnboardCompletePage } from '@/features/onboard/onboard-complete-page';
+import { createFileRoute } from '@tanstack/react-router';
+
+export const Route = createFileRoute('/onboard/complete')({
+  component: OnboardCompletePage,
+});