feat: 完善审批退回流程与报销申请关联

后端优化报销单访问策略和常量定义，增强退回原因和审批状态
流转，前端完善退回对话框和审批交互组件，新增报销申请关联
模型，优化文档中心行数据和审批收件箱工具函数，增强引导
流程和会话模型，补充单元测试覆盖。

web/src/utils/approvalInbox.js

@@ -1,23 +1,18 @@
 import { mapExpenseClaimToRequest } from '../composables/useRequests.js'
 import {
   canApproveLeaderExpenseClaims,
-  canManageExpenseClaims,
+  isCurrentDirectManagerForRequest,
+  isCurrentRequestApplicant,
   isFinanceUser
 } from './accessControl.js'
 
 export function canProcessApprovalRequest(request, currentUser) {
   const node = String(request?.workflowNode || '').trim()
-  const currentName = String(currentUser?.name || '').trim()
-  const applicantName = String(request?.person || request?.employeeName || '').trim()
 
-  if (currentName && applicantName && currentName === applicantName) {
+  if (isCurrentRequestApplicant(request, currentUser)) {
     return false
   }
 
-  if (canManageExpenseClaims(currentUser)) {
-    return true
-  }
-
   if (isFinanceUser(currentUser) && node.includes('财务')) {
     return true
   }
@@ -29,7 +24,11 @@ export function canProcessApprovalRequest(request, currentUser) {
     || node.includes('负责人审批')
   )
 
-  return canApproveLeaderExpenseClaims(currentUser) && isLeaderApprovalNode
+  return (
+    canApproveLeaderExpenseClaims(currentUser)
+    && isLeaderApprovalNode
+    && isCurrentDirectManagerForRequest(request, currentUser)
+  )
 }
 
 export function listPendingApprovalRequests(claimsPayload, currentUser) {