fix(reward-service): 修复 DI 依赖注入错误

问题: RewardCalculationService 无法解析依赖
- DomainModule 未导入 InfrastructureModule
- service clients 使用 useClass 导致创建新实例时缺少依赖

解决方案:
1. DomainModule 导入 InfrastructureModule
2. InfrastructureModule 中:
   - 先注册具体的 client 类 (ReferralServiceClient, AuthorizationServiceClient)
   - 然后用 useExisting 提供 token 别名
   - 这样确保使用同一个实例，包含所有依赖

参考: leaderboard-service 的修复方案

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

backend/services/reward-service/src/domain/domain.module.ts

@@ -1,8 +1,10 @@
 import { Module } from '@nestjs/common';
 import { RewardCalculationService } from './services/reward-calculation.service';
 import { RewardExpirationService } from './services/reward-expiration.service';
+import { InfrastructureModule } from '../infrastructure/infrastructure.module';
 
 @Module({
+  imports: [InfrastructureModule],
   providers: [
     RewardCalculationService,
     RewardExpirationService,

backend/services/reward-service/src/infrastructure/infrastructure.module.ts

@@ -24,15 +24,19 @@ import { REFERRAL_SERVICE_CLIENT, AUTHORIZATION_SERVICE_CLIENT } from '../domain
       provide: REWARD_SUMMARY_REPOSITORY,
       useClass: RewardSummaryRepositoryImpl,
     },
+    // Register concrete classes first
+    ReferralServiceClient,
+    AuthorizationServiceClient,
+    WalletServiceClient,
+    // Then provide token aliases using useExisting
     {
       provide: REFERRAL_SERVICE_CLIENT,
-      useClass: ReferralServiceClient,
+      useExisting: ReferralServiceClient,
     },
     {
       provide: AUTHORIZATION_SERVICE_CLIENT,
-      useClass: AuthorizationServiceClient,
+      useExisting: AuthorizationServiceClient,
     },
-    WalletServiceClient,
   ],
   exports: [
     PrismaService,