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/payment-gateway.interface.ts

@@ -0,0 +1,46 @@
+import { type PaymentProvider } from '@prisma/client';
+
+export const PAYMENT_GATEWAY_FACTORY = Symbol('PAYMENT_GATEWAY_FACTORY');
+
+export interface CreatePaymentUrlParams {
+  orderId: string;
+  amountVND: bigint;
+  description: string;
+  returnUrl: string;
+  ipAddress: string;
+}
+
+export interface CreatePaymentUrlResult {
+  paymentUrl: string;
+  providerTxId: string;
+}
+
+export interface CallbackVerifyResult {
+  isValid: boolean;
+  orderId: string;
+  providerTxId: string;
+  isSuccess: boolean;
+  rawData: Record<string, unknown>;
+}
+
+export interface RefundParams {
+  providerTxId: string;
+  amountVND: bigint;
+  reason: string;
+}
+
+export interface RefundResult {
+  success: boolean;
+  refundTxId: string | null;
+}
+
+export interface IPaymentGateway {
+  readonly provider: PaymentProvider;
+  createPaymentUrl(params: CreatePaymentUrlParams): Promise<CreatePaymentUrlResult>;
+  verifyCallback(data: Record<string, string>): CallbackVerifyResult;
+  refund(params: RefundParams): Promise<RefundResult>;
+}
+
+export interface IPaymentGatewayFactory {
+  getGateway(provider: PaymentProvider): IPaymentGateway;
+}