feat(web): 设置中心缓存管理与文件预览资产工具

- 新增 documentPreviewAssets 工具，统一从 URL/Blob/File 推断预览类型（image/pdf/file/unsupported）
- SettingsView/SettingsView.js/settingsModelHelper 新增系统缓存管理区块，调用 /settings/cache/clear 并展示清理结果；useSettings/services 适配
- WorkbenchAiFilePreviewDialog/useWorkbenchAiFilePreview 接入预览资产工具，workbenchAiComposerModel 调整文件处理
- ReceiptFolder/LogDetailView/DigitalEmployeeWorkRecords/travelReimbursementAttachmentModel 配套适配
- 新增 settings-cache-management-section 测试，更新 settings-llm/rendering/receipt-folder-view/composer-components/attachment-association 测试

web/src/services/settings.js

@@ -17,3 +17,9 @@ export function testModelConnectivity(payload) {
     body: JSON.stringify(payload)
   })
 }
+
+export function clearSystemCaches() {
+  return apiRequest('/settings/cache/clear', {
+    method: 'POST'
+  })
+}