feat(server): add auth, user, and studio modules

Auth: WeChat login, JWT, roles guard (24 tests passing)
User: profile CRUD, training stats with month/total calculations
Studio: config management with auto-default creation

packages/server/src/auth/dto/login.dto.ts

@@ -0,0 +1,7 @@
+import { IsString, IsNotEmpty } from 'class-validator'
+
+export class LoginDto {
+  @IsString()
+  @IsNotEmpty()
+  code!: string
+}