feat: add pricing checkout flow, MFA type fixes, and Wave 13 audit docs

- Pricing page: enhanced with checkout modal integration, plan
  comparison table, and subscription funnel
- Payment return page: new VNPay/MoMo callback handler
- Subscription components: new checkout-modal with payment method
  selection (VNPay, MoMo, ZaloPay)
- API modules: type-safe PII encryption, improved error handling in
  MFA/auth/payments/analytics/search/notifications modules
- Audit docs: comprehensive Wave 13 platform assessment, pricing
  audit, production readiness checklist
- Updated PROJECT_TRACKER with Wave 13 status

Co-Authored-By: Paperclip <noreply@paperclip.ing>

apps/web/components/subscription/index.ts

@@ -0,0 +1 @@
+export { CheckoutModal } from './checkout-modal';