feat(payments): implement Payments module with VNPay, MoMo, ZaloPay integration

Implement complete payment processing module following DDD + CQRS patterns:

- Domain layer: PaymentEntity aggregate, Money value object, domain events
- Infrastructure: PrismaPaymentRepository, VnpayService, MomoService, ZalopayService
- PaymentGatewayFactory pattern for provider abstraction
- CQRS Commands: CreatePayment, HandleCallback, RefundPayment
- CQRS Queries: GetPaymentStatus, ListTransactions
- Callback/webhook endpoints with signature verification and idempotency
- 23 unit tests covering domain, VNPay service, and gateway factory

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

apps/api/src/modules/payments/infrastructure/services/index.ts

@@ -0,0 +1,14 @@
+export {
+  PAYMENT_GATEWAY_FACTORY,
+  type IPaymentGateway,
+  type IPaymentGatewayFactory,
+  type CreatePaymentUrlParams,
+  type CreatePaymentUrlResult,
+  type CallbackVerifyResult,
+  type RefundParams,
+  type RefundResult,
+} from './payment-gateway.interface';
+export { PaymentGatewayFactory } from './payment-gateway.factory';
+export { VnpayService } from './vnpay.service';
+export { MomoService } from './momo.service';
+export { ZalopayService } from './zalopay.service';