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/app.ts

@@ -35,7 +35,7 @@ import { userImportRoutes } from './features/user-import';
 import { ownershipCostsRoutes } from './features/ownership-costs';
 import { subscriptionsRoutes, donationsRoutes, webhooksRoutes } from './features/subscriptions';
 import { ocrRoutes } from './features/ocr';
-import { emailIngestionWebhookRoutes } from './features/email-ingestion';
+import { emailIngestionWebhookRoutes, emailIngestionRoutes } from './features/email-ingestion';
 import { pool } from './core/config/database';
 import { configRoutes } from './core/config/config.routes';
 
@@ -154,6 +154,7 @@ async function buildApp(): Promise<FastifyInstance> {
   await app.register(donationsRoutes, { prefix: '/api' });
   await app.register(webhooksRoutes, { prefix: '/api' });
   await app.register(emailIngestionWebhookRoutes, { prefix: '/api' });
+  await app.register(emailIngestionRoutes, { prefix: '/api' });
   await app.register(ocrRoutes, { prefix: '/api' });
   await app.register(configRoutes, { prefix: '/api' });