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/application/index.ts

@@ -0,0 +1,11 @@
+export { CreatePaymentCommand } from './commands/create-payment/create-payment.command';
+export { CreatePaymentHandler, type CreatePaymentResult } from './commands/create-payment/create-payment.handler';
+export { HandleCallbackCommand } from './commands/handle-callback/handle-callback.command';
+export { HandleCallbackHandler, type HandleCallbackResult } from './commands/handle-callback/handle-callback.handler';
+export { RefundPaymentCommand } from './commands/refund-payment/refund-payment.command';
+export { RefundPaymentHandler, type RefundPaymentResult } from './commands/refund-payment/refund-payment.handler';
+
+export { GetPaymentStatusQuery } from './queries/get-payment-status/get-payment-status.query';
+export { GetPaymentStatusHandler, type PaymentStatusDto } from './queries/get-payment-status/get-payment-status.handler';
+export { ListTransactionsQuery } from './queries/list-transactions/list-transactions.query';
+export { ListTransactionsHandler, type TransactionListDto } from './queries/list-transactions/list-transactions.handler';