feat(web): AI 工作台文件预览/附件关联任务与草稿分支

- 新增 WorkbenchAiFilePreviewDialog 附件预览对话框及 useWorkbenchAiFilePreview，附件支持点击预览
- 新增 attachmentAssociationJobs/linkedReimbursementDraftJobs 前端服务与对应 composable，接入后台任务轮询与状态展示
- 新增 travelReimbursementDraftBranchModel 草稿分支模型，报销关联门控支持跳过/选择草稿
- PersonalWorkbenchAiMode 及各 composable（expense/document/steward/application-preview/attachment-association）重构适配，WorkbenchAiComposer/FileStrip 样式与交互完善
- DocumentsCenter/ReceiptFolder/TravelReimbursementCreate 等视图及 scripts 重构，风险/差旅规划/审批等工具适配
- 新增/更新前端测试：application-result-card、reimbursement-list-preview-fetch、guided-flow、composer-components 等

web/tests/backend-health-timeout.test.mjs

@@ -9,6 +9,10 @@ const routerScript = readFileSync(
   fileURLToPath(new URL('../src/router/index.js', import.meta.url)),
   'utf8'
 )
+const backendUnavailableScript = readFileSync(
+  fileURLToPath(new URL('../src/views/scripts/BackendUnavailableRouteView.js', import.meta.url)),
+  'utf8'
+)
 
 test('app route guard allows stale healthy state when health check times out', () => {
   assert.match(routerScript, /checkBackendHealth\(\{\s*allowStaleOnTimeout:\s*true\s*\}\)/)
@@ -49,3 +53,11 @@ test('backend health timeout does not block app rendering when stale fallback is
     global.fetch = originalFetch
   }
 })
+
+test('backend unavailable page automatically recovers after service startup race', () => {
+  assert.match(backendUnavailableScript, /onMounted\(\s*\(\)\s*=>\s*\{/)
+  assert.match(backendUnavailableScript, /startAutoRecover\(\)/)
+  assert.match(backendUnavailableScript, /globalThis\.setInterval/)
+  assert.match(backendUnavailableScript, /router\.replace\(loggedIn\.value \? resolveEntryRoute\(\) : \{ name: 'login' \}\)/)
+  assert.match(backendUnavailableScript, /onBeforeUnmount\(\s*\(\)\s*=>\s*\{/)
+})