refactor: 重构解决方案相关Mapper

- 空值处理与类型控制：为关系型字段添加空值处理与类型控制逻辑
- 目录结构调整：分离SolutionList与Solution相关的Mapper为不同的文件

server/mappers/solutionMapper.test.ts

@@ -1,56 +1,5 @@
 import { describe, test, expect } from 'vitest';
-import { toSolutionListView, toSolutionView } from './solutionMapper';
-
-/**
- * 单元测试: toSolutionListView
- */
-describe('toSolutionListView', () => {
-  const baseData: Solution = {
-    id: 1,
-    translations: [
-      { id: 1, title: 'Solution Title', summary: 'Solution Summary' },
-    ],
-    type: {
-      id: 1,
-      translations: [{ id: 1, name: 'Type Name' }],
-      sort: 1,
-    },
-  };
-  test('convert raw data to SolutionListView correctly', () => {
-    const rawData: Solution = { ...baseData };
-
-    expect(toSolutionListView(rawData)).toEqual({
-      id: '1',
-      title: 'Solution Title',
-      summary: 'Solution Summary',
-      solution_type: {
-        id: '1',
-        name: 'Type Name',
-        sort: 1,
-      },
-      cover: '',
-    });
-  });
-
-  test('convert raw data with missing translations', () => {
-    const rawData: Solution = {
-      ...baseData,
-      translations: [],
-    };
-
-    expect(toSolutionListView(rawData)).toEqual({
-      id: '1',
-      title: '',
-      summary: '',
-      solution_type: {
-        id: '1',
-        name: 'Type Name',
-        sort: 1,
-      },
-      cover: '',
-    });
-  });
-});
+import { toSolutionView } from './solutionMapper';
 
 /**
  * 单元测试: toSolutionView