feat: 实现出差申请页面

- 创建出差申请表单，包含出差事由、行程明细、审批人选择
- 实现行程明细的增删改功能，支持开始/结束时间、出发地、目的地等
- 添加单程/往返类型选择和交通工具下拉选择
- 实现自动计算行程时长和总时长
- 创建审批人和抄送人选择页面
- 添加前后端API接口定义
- 更新i18n国际化翻译
- 整理开发文档和UI设计图

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/router/index.tsx

@@ -5,6 +5,8 @@ import Apps from '@/pages/apps'
 import BusinessTripList from '@/pages/business-trip/list'
 import BusinessTripApply from '@/pages/business-trip/apply'
 import BusinessTripDetail from '@/pages/business-trip/detail'
+import SelectApprover from '@/pages/business-trip/select-approver'
+import SelectCc from '@/pages/business-trip/select-cc'
 import Profile from '@/pages/profile'
 import Login from '@/pages/login'
 
@@ -18,6 +20,8 @@ const router = createBrowserRouter([
       { path: 'apps', element: <Apps /> },
       { path: 'business-trip', element: <BusinessTripList /> },
       { path: 'business-trip/apply', element: <BusinessTripApply /> },
+      { path: 'business-trip/apply/select-approver', element: <SelectApprover /> },
+      { path: 'business-trip/apply/select-cc', element: <SelectCc /> },
       { path: 'business-trip/:id', element: <BusinessTripDetail /> },
       { path: 'profile', element: <Profile /> },
     ],