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/identity/auth.dto.ts

@@ -0,0 +1,24 @@
+import { IsString, MinLength } from 'class-validator';
+import { ApiProperty } from '@nestjs/swagger';
+
+export class LoginDto {
+  @ApiProperty()
+  @IsString()
+  username!: string;
+
+  @ApiProperty()
+  @IsString()
+  @MinLength(1)
+  password!: string;
+}
+
+export class ChangePasswordDto {
+  @ApiProperty()
+  @IsString()
+  oldPassword!: string;
+
+  @ApiProperty()
+  @IsString()
+  @MinLength(8)
+  newPassword!: string;
+}