feat(api): add Vietnam validators and migrate payment services to ConfigService

- Create custom class-validator decorators: IsVietnamPhone, IsVietnamDistrict, IsVND
- Replace process.env/requireEnv() with NestJS ConfigService DI in VNPay, MoMo, ZaloPay services
- Update all payment infrastructure tests with ConfigService mocks (42 tests passing)

TEC-1569

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/api/src/modules/payments/infrastructure/services/zalopay.service.ts

@@ -1,5 +1,6 @@
 import * as crypto from 'crypto';
 import { Injectable, Logger } from '@nestjs/common';
+import { ConfigService } from '@nestjs/config';
 import { type PaymentProvider } from '@prisma/client';
 import {
   type IPaymentGateway,
@@ -10,33 +11,21 @@ import {
   type RefundResult,
 } from './payment-gateway.interface';
 
-function requireEnv(key: string): string {
-  const value = process.env[key];
-  if (!value) {
-    throw new Error(`Missing required environment variable: ${key}`);
-  }
-  return value;
-}
-
 @Injectable()
 export class ZalopayService implements IPaymentGateway {
   private readonly logger = new Logger(ZalopayService.name);
   readonly provider: PaymentProvider = 'ZALOPAY';
 
-  private get appId(): string {
-    return requireEnv('ZALOPAY_APP_ID');
-  }
+  private readonly appId: string;
+  private readonly key1: string;
+  private readonly key2: string;
+  private readonly endpoint: string;
 
-  private get key1(): string {
-    return requireEnv('ZALOPAY_KEY1');
-  }
-
-  private get key2(): string {
-    return requireEnv('ZALOPAY_KEY2');
-  }
-
-  private get endpoint(): string {
-    return process.env['ZALOPAY_ENDPOINT'] ?? 'https://sb-openapi.zalopay.vn/v2';
+  constructor(private readonly config: ConfigService) {
+    this.appId = this.config.getOrThrow<string>('ZALOPAY_APP_ID');
+    this.key1 = this.config.getOrThrow<string>('ZALOPAY_KEY1');
+    this.key2 = this.config.getOrThrow<string>('ZALOPAY_KEY2');
+    this.endpoint = this.config.get<string>('ZALOPAY_ENDPOINT', 'https://sb-openapi.zalopay.vn/v2');
   }
 
   async createPaymentUrl(params: CreatePaymentUrlParams): Promise<CreatePaymentUrlResult> {