feat: 完善报销单审批流程及退回原因追踪

新增直属领导审批通过接口和审批待办列表查询，报销单退回
支持原因码分类和审批环节标记，优化票据附件去重和路径
回退查找，前端新增退回原因对话框、审批收件箱和工作台
图标组件，补充工具函数和单元测试覆盖。

web/src/services/reimbursements.js

@@ -4,6 +4,10 @@ export function fetchExpenseClaims() {
   return apiRequest('/reimbursements/claims')
 }
 
+export function fetchApprovalExpenseClaims() {
+  return apiRequest('/reimbursements/claims/approvals')
+}
+
 export function fetchExpenseClaimDetail(claimId) {
   return apiRequest(`/reimbursements/claims/${encodeURIComponent(String(claimId || '').trim())}`)
 }
@@ -94,6 +98,13 @@ export function returnExpenseClaim(claimId, payload = {}) {
   })
 }
 
+export function approveExpenseClaim(claimId, payload = {}) {
+  return apiRequest(`/reimbursements/claims/${encodeURIComponent(String(claimId || '').trim())}/approve`, {
+    method: 'POST',
+    body: JSON.stringify(payload)
+  })
+}
+
 export function deleteExpenseClaim(claimId) {
   return apiRequest(`/reimbursements/claims/${encodeURIComponent(String(claimId || '').trim())}`, {
     method: 'DELETE'