feat: add vehicle count column to admin user management

Add a new "Vehicles" column to the admin user management table showing
the count of active vehicles for each user.

Backend changes:
- Add vehicleCount to UserWithAdminStatus type
- Add SQL subquery to count active vehicles (is_active=true, not deleted)
- Add vehicleCount as sortable column option

Frontend changes:
- Add Vehicles column to desktop table (between Tier and Status)
- Add VehicleCountBadge component to mobile user cards
- Update ManagedUser type with vehicleCount field

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

frontend/src/features/admin/mobile/AdminUsersMobileScreen.tsx

@@ -81,6 +81,13 @@ const StatusBadge: React.FC<{ active: boolean }> = ({ active }) => (
   </span>
 );
 
+// Vehicle count badge component
+const VehicleCountBadge: React.FC<{ count: number }> = ({ count }) => (
+  <span className="px-2 py-1 rounded-full text-xs font-medium bg-slate-100 text-slate-700">
+    {count} {count === 1 ? 'vehicle' : 'vehicles'}
+  </span>
+);
+
 export const AdminUsersMobileScreen: React.FC = () => {
   const { isAdmin, loading: adminLoading } = useAdminAccess();
 
@@ -453,6 +460,7 @@ export const AdminUsersMobileScreen: React.FC = () => {
                       )}
                       <div className="flex flex-wrap gap-2 mt-2">
                         <TierBadge tier={user.subscriptionTier} />
+                        <VehicleCountBadge count={user.vehicleCount} />
                         <StatusBadge active={!user.deactivatedAt} />
                         {user.isAdmin && (
                           <span className="px-2 py-1 rounded-full text-xs font-medium bg-amber-100 text-amber-700">

frontend/src/features/admin/types/admin.types.ts

@@ -237,6 +237,7 @@ export interface ManagedUser {
   updatedAt: string;
   isAdmin: boolean;
   adminRole: 'admin' | 'super_admin' | null;
+  vehicleCount: number;
 }
 
 // List users response with pagination
@@ -254,7 +255,7 @@ export interface ListUsersParams {
   search?: string;
   tier?: SubscriptionTier;
   status?: 'active' | 'deactivated' | 'all';
-  sortBy?: 'email' | 'createdAt' | 'displayName' | 'subscriptionTier';
+  sortBy?: 'email' | 'createdAt' | 'displayName' | 'subscriptionTier' | 'vehicleCount';
   sortOrder?: 'asc' | 'desc';
 }
 

frontend/src/pages/admin/AdminUsersPage.tsx

@@ -420,6 +420,7 @@ export const AdminUsersPage: React.FC = () => {
                     <TableCell>Email</TableCell>
                     <TableCell>Display Name</TableCell>
                     <TableCell>Tier</TableCell>
+                    <TableCell>Vehicles</TableCell>
                     <TableCell>Status</TableCell>
                     <TableCell>Admin</TableCell>
                     <TableCell>Created</TableCell>
@@ -450,6 +451,7 @@ export const AdminUsersPage: React.FC = () => {
                           </Select>
                         </FormControl>
                       </TableCell>
+                      <TableCell>{user.vehicleCount}</TableCell>
                       <TableCell>
                         <Chip
                           label={user.deactivatedAt ? 'Deactivated' : 'Active'}