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/data/email-ingestion.repository.ts

@@ -194,6 +194,33 @@ export class EmailIngestionRepository {
     }
   }
 
+  async getPendingAssociationById(associationId: string): Promise<PendingVehicleAssociation | null> {
+    try {
+      const res = await this.db.query(
+        `SELECT * FROM pending_vehicle_associations WHERE id = $1`,
+        [associationId]
+      );
+      return res.rows[0] ? this.mapPendingAssociationRow(res.rows[0]) : null;
+    } catch (error) {
+      logger.error('Error fetching pending association by id', { error, associationId });
+      throw error;
+    }
+  }
+
+  async getPendingAssociationCount(userId: string): Promise<number> {
+    try {
+      const res = await this.db.query(
+        `SELECT COUNT(*)::int AS count FROM pending_vehicle_associations
+        WHERE user_id = $1 AND status = 'pending'`,
+        [userId]
+      );
+      return res.rows[0]?.count ?? 0;
+    } catch (error) {
+      logger.error('Error counting pending associations', { error, userId });
+      throw error;
+    }
+  }
+
   async getPendingAssociations(userId: string): Promise<PendingVehicleAssociation[]> {
     try {
       const res = await this.db.query(