refactor: 重构产品相关Mapper

- 空值处理与类型控制：为相关关系型字段的数据处理添加空值处理与类型控制
- 调整目录结构：将文件目录按照实际查询划分为Product和ProductList两个文件

server/mappers/questionMapper.test.ts

@@ -1,9 +1,5 @@
 import { describe, expect, test } from 'vitest';
-import {
-  toProductQuestionView,
-  toQuestionListView,
-  toQuestionTypeView,
-} from './questionMapper';
+import { toQuestionListView, toQuestionTypeView } from './questionMapper';
 
 /**
  * 单元测试: toQuestionTypeView
@@ -47,42 +43,6 @@ describe('toQuestionTypeView', () => {
   });
 });
 
-/**
- * 单元测试: toProductQuestionView
- */
-describe('toProductQuestionView', () => {
-  const baseData: Question = {
-    id: 1,
-    translations: [
-      { id: 1, title: 'Question Title', content: 'Question Answer' },
-    ],
-  };
-  test('convert raw data to ProductQuestionView correctly', () => {
-    const rawData: Question = {
-      ...baseData,
-    };
-
-    expect(toProductQuestionView(rawData)).toEqual({
-      id: '1',
-      title: 'Question Title',
-      content: 'Question Answer',
-    });
-  });
-
-  test('convert raw data with missing translations', () => {
-    const rawData: Question = {
-      ...baseData,
-      translations: [],
-    };
-
-    expect(toProductQuestionView(rawData)).toEqual({
-      id: '1',
-      title: '',
-      content: '',
-    });
-  });
-});
-
 /**
  * 单元测试: toQuestionListView
  */