feat: Add Promo Interest column to admin users page

- Backend: Include promo_preferred_maker, promo_preferred_model, promo_email_enabled in admin/users API
- Frontend: Add AdminUser interface fields
- Admin UI: Display Promo Interest column with maker/model and email alert status

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/src/lib/api.ts

@@ -1203,6 +1203,9 @@ export interface AdminUser {
   is_dealer: boolean;
   referral_code?: string;
   referred_by?: string;
+  promo_preferred_maker?: string;
+  promo_preferred_model?: string;
+  promo_email_enabled?: boolean;
   created_at?: string;
 }