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/tests/requestViewModel.test.mjs

@@ -0,0 +1,33 @@
+import assert from 'node:assert/strict'
+import test from 'node:test'
+
+import { normalizeRequestForUi } from '../src/utils/requestViewModel.js'
+
+test('normalizes backend approval_stage for in-progress claim details', () => {
+  const request = normalizeRequestForUi({
+    id: 'EXP-202605-001',
+    claim_id: 'claim-1',
+    status: 'submitted',
+    approval_stage: '直属领导审批',
+    expense_type: 'transport',
+    amount: 88
+  })
+
+  assert.equal(request.approvalKey, 'in_progress')
+  assert.equal(request.node, '直属领导审批')
+})
+
+test('normalizes returned backend claims as editable pending submission', () => {
+  const request = normalizeRequestForUi({
+    id: 'EXP-202605-002',
+    claim_id: 'claim-2',
+    status: 'returned',
+    approval_stage: '待提交',
+    expense_type: 'transport',
+    amount: 66
+  })
+
+  assert.equal(request.approvalKey, 'supplement')
+  assert.equal(request.approvalStatus, '待提交')
+  assert.equal(request.node, '待提交')
+})