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/i18n/locales/zh.json

@@ -68,8 +68,10 @@
     "startDate": "开始日期",
     "endDate": "结束日期",
     "duration": "出差天数",
+    "totalDuration": "出差总时长",
     "reason": "出差事由",
-    "budget": "预算金额",
+    "budget": "预计费用",
+    "estimatedCost": "预计费用",
     "submitter": "申请人",
     "submitTime": "申请时间",
     "approver": "审批人",
@@ -78,7 +80,30 @@
     "confirmSubmit": "确认提交出差申请？",
     "confirmCancel": "确认撤销此申请？",
     "submitSuccess": "提交成功",
-    "cancelSuccess": "撤销成功"
+    "cancelSuccess": "撤销成功",
+    "itinerary": "行程明细",
+    "itineraryDate": "日期",
+    "itineraryStartTime": "开始时间",
+    "itineraryEndTime": "结束时间",
+    "itineraryDeparture": "出发地",
+    "itineraryDestination": "目的地",
+    "itineraryTransport": "交通工具",
+    "itineraryAccommodation": "住宿安排",
+    "itineraryRemark": "备注",
+    "tripType": "行程类型",
+    "tripTypeOneWay": "单程",
+    "tripTypeRoundTrip": "往返",
+    "addItinerary": "添加行程",
+    "selectApprovers": "选择审批人",
+    "selectCc": "选择抄送",
+    "approvers": "审批人",
+    "cc": "抄送",
+    "pleaseEnterReason": "请输入出差事由",
+    "pleaseSelectDate": "请选择日期",
+    "pleaseEnterDestination": "请输入目的地",
+    "pleaseEnterCost": "请输入预计费用",
+    "noItinerary": "暂无行程",
+    "removeItinerary": "删除行程"
   },
   "approval": {
     "title": "审批管理",