fix: 修复选择审批人后抄送人消失的问题

- 使用 useRef 防止默认审批人/抄送人数据重复加载
- 确保从选择页面返回时，另一类型的数据不受影响

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

frontend/src/pages/business-trip/apply.tsx

@@ -87,7 +87,11 @@ export default function BusinessTripApply() {
   const hasRestoredRef = useRef(false)
 
   // 加载默认审批人和抄送人（仅在首次加载且没有草稿数据时）
+  const defaultLoadedRef = useRef(false)
   useEffect(() => {
+    // 防止重复加载
+    if (defaultLoadedRef.current) return
+
     const loadDefaultApprovers = async () => {
       // 如果已经有存储的草稿数据，不加载默认值
       if (sessionStorage.getItem('businessTripDraft')) {
@@ -112,13 +116,14 @@ export default function BusinessTripApply() {
           setCcUsers(defaultData.cc_users)
           sessionStorage.setItem('selectedCc', JSON.stringify(defaultData.cc_users))
         }
+        defaultLoadedRef.current = true
       } catch (error) {
         console.error('Failed to load default approvers:', error)
       }
     }
 
     loadDefaultApprovers()
-  }, [])
+  }, [location.state?.fromSelection])
 
   // 处理从选择页面返回的数据和草稿恢复
   useEffect(() => {

frontend/src/pages/business-trip/select-approver.tsx

@@ -1,4 +1,4 @@
-import { useState, useEffect } from 'react'
+import { useState, useEffect, useRef } from 'react'
 import { useNavigate, useLocation } from 'react-router-dom'
 import { useTranslation } from 'react-i18next'
 import { NavBar, SearchBar, Button, Toast, Empty } from 'antd-mobile'
@@ -39,10 +39,13 @@ export default function SelectUserPage() {
   const [loading, setLoading] = useState(false)
   const [hasMore, setHasMore] = useState(true)
   const [page, setPage] = useState(1)
-  const [defaultLoaded, setDefaultLoaded] = useState(false)
+  const initialLoadedRef = useRef(false)
 
   // 获取初始选中的用户（从 sessionStorage 或后端默认配置）
   const loadInitialSelected = async () => {
+    // 防止重复加载
+    if (initialLoadedRef.current) return
+
     const type = location.state?.type || 'approver'
     const storageKey = type === 'approver' ? 'selectedApprovers' : 'selectedCc'
 
@@ -53,6 +56,7 @@ export default function SelectUserPage() {
         const parsed = JSON.parse(storedData)
         if (parsed.length > 0) {
           setSelectedUsers(parsed)
+          initialLoadedRef.current = true
           return
         }
       } catch (e) {
@@ -72,6 +76,7 @@ export default function SelectUserPage() {
       // 获取失败时设置为空数组
       setSelectedUsers([])
     }
+    initialLoadedRef.current = true
   }
 
   // 加载用户列表