feat(dc): Complete Tool B frontend development with UI optimization

- Implement Tool B 5-step workflow (upload, schema, processing, verify, result)
- Add back navigation button to Portal
- Optimize Step 2 field list styling to match prototype
- Fix step 3 label: 'dual-blind' to 'dual-model'
- Create API service layer with 7 endpoints
- Integrate Tool B route into DC module
- Add comprehensive TypeScript types

Components (~1100 lines):
- index.tsx: Main Tool B entry with state management
- Step1Upload.tsx: File upload and health check
- Step2Schema.tsx: Smart template configuration
- Step3Processing.tsx: Dual-model extraction progress
- Step4Verify.tsx: Conflict verification workbench
- Step5Result.tsx: Result display
- StepIndicator.tsx: Step progress component
- api/toolB.ts: API service layer

Status: Frontend complete, ready for API integration

backend/scripts/check-dc-tables.mjs

@@ -197,3 +197,4 @@ async function checkDCTables() {
 // 执行检查
 checkDCTables();
 
+