feat(payments): improve VNPay, MoMo, ZaloPay services with ConfigService

Migrate payment gateway services from hardcoded config to NestJS
ConfigService injection. Improve payment handler error handling and
update gateway factory specs.

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

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

@@ -1,3 +1,4 @@
 export { PaymentsModule } from './payments.module';
 export { PAYMENT_REPOSITORY, type IPaymentRepository } from './domain/repositories/payment.repository';
 export { PAYMENT_GATEWAY_FACTORY, type IPaymentGatewayFactory } from './infrastructure/services/payment-gateway.interface';
+export { PaymentCompletedEvent } from './domain/events/payment-completed.event';