feat: add pending vehicle association resolution UI (refs #160)

Backend: Add authenticated endpoints for pending association CRUD
(GET/POST/DELETE /api/email-ingestion/pending). Service methods for
resolving (creates fuel/maintenance record) and dismissing associations.

Frontend: New email-ingestion feature with types, API client, hooks,
PendingAssociationBanner (dashboard), PendingAssociationList, and
ResolveAssociationDialog. Mobile-first responsive with 44px touch
targets and full-screen dialogs on small screens.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/src/features/email-ingestion/index.ts

@@ -3,7 +3,7 @@
  * @ai-context Exports webhook routes, services, and types for Resend inbound email processing
  */
 
-export { emailIngestionWebhookRoutes } from './api/email-ingestion.routes';
+export { emailIngestionWebhookRoutes, emailIngestionRoutes } from './api/email-ingestion.routes';
 export { EmailIngestionService } from './domain/email-ingestion.service';
 export { EmailIngestionRepository } from './data/email-ingestion.repository';
 export { ReceiptClassifier } from './domain/receipt-classifier';