重构 API 为 8 领域 + 应用层架构

将后端模块拆分为 domains、applications、shared 三层，结算计算器移入 domain 纯函数目录，API 路径与测试保持不变。

Co-authored-by: Cursor <cursoragent@cursor.com>

apps/api/src/domains/settlement/settlement.module.ts

@@ -0,0 +1,11 @@
+import { Module } from '@nestjs/common';
+import { SettlementService } from './settlement.service';
+import { WalletModule } from '../ledger/wallet.module';
+import { AgentsModule } from '../agent/agents.module';
+
+@Module({
+  imports: [WalletModule, AgentsModule],
+  providers: [SettlementService],
+  exports: [SettlementService],
+})
+export class SettlementModule {}