feat: Add admin vehicle management and profile vehicles display (refs #11)

- Add GET /api/admin/stats endpoint for Total Vehicles widget
- Add GET /api/admin/users/:auth0Sub/vehicles endpoint for user vehicle list
- Update AdminUsersPage with Total Vehicles stat and expandable vehicle rows
- Add My Vehicles section to SettingsPage (desktop) and MobileSettingsScreen
- Update AdminUsersMobileScreen with stats header and vehicle expansion
- Add defense-in-depth admin checks and error handling
- Update admin README documentation

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

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

frontend/src/features/settings/mobile/MobileSettingsScreen.tsx

@@ -5,6 +5,7 @@ import { MobileContainer } from '../../../shared-minimal/components/mobile/Mobil
 import { useSettings } from '../hooks/useSettings';
 import { useProfile, useUpdateProfile } from '../hooks/useProfile';
 import { useExportUserData } from '../hooks/useExportUserData';
+import { useVehicles } from '../../vehicles/hooks/useVehicles';
 import { useAdminAccess } from '../../../core/auth/useAdminAccess';
 import { useNavigationStore } from '../../../core/store';
 import { DeleteAccountModal } from './DeleteAccountModal';
@@ -80,6 +81,7 @@ export const MobileSettingsScreen: React.FC = () => {
   const { data: profile, isLoading: profileLoading } = useProfile();
   const updateProfileMutation = useUpdateProfile();
   const exportMutation = useExportUserData();
+  const { data: vehicles, isLoading: vehiclesLoading } = useVehicles();
   const { isAdmin, loading: adminLoading } = useAdminAccess();
   const [showDataExport, setShowDataExport] = useState(false);
   const [showDeleteConfirm, setShowDeleteConfirm] = useState(false);
@@ -316,6 +318,58 @@ export const MobileSettingsScreen: React.FC = () => {
           </div>
         </GlassCard>
 
+        {/* My Vehicles Section */}
+        <GlassCard padding="md">
+          <div>
+            <div className="flex justify-between items-center mb-4">
+              <div className="flex items-center gap-2">
+                <svg className="w-5 h-5 text-primary-500" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+                  <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M19 4H5c-1.1 0-2 .9-2 2v10c0 1.1.9 2 2 2h4l3 3 3-3h4c1.1 0 2-.9 2-2V6c0-1.1-.9-2-2-2zM8 11V9h8v2m-8 4v-2h5v2" />
+                </svg>
+                <h2 className="text-lg font-semibold text-slate-800 dark:text-avus">
+                  My Vehicles
+                </h2>
+                {!vehiclesLoading && vehicles && (
+                  <span className="text-sm text-slate-500 dark:text-titanio">({vehicles.length})</span>
+                )}
+              </div>
+              <button
+                onClick={() => navigateToScreen('Vehicles')}
+                className="px-3 py-1.5 bg-primary-500 text-white rounded-lg text-sm font-medium hover:bg-primary-600 transition-colors dark:bg-primary-600 dark:hover:bg-primary-700"
+                style={{ minHeight: '44px', minWidth: '44px' }}
+              >
+                Manage
+              </button>
+            </div>
+
+            {vehiclesLoading ? (
+              <div className="flex justify-center py-4">
+                <div className="animate-spin rounded-full h-6 w-6 border-b-2 border-primary-500"></div>
+              </div>
+            ) : !vehicles?.length ? (
+              <p className="text-sm text-slate-500 dark:text-titanio py-2">
+                No vehicles registered. Add your first vehicle to get started.
+              </p>
+            ) : (
+              <div className="space-y-2">
+                {vehicles.map((vehicle) => (
+                  <div
+                    key={vehicle.id}
+                    className="p-3 bg-slate-50 dark:bg-nero rounded-lg"
+                  >
+                    <p className="font-medium text-slate-800 dark:text-avus">
+                      {vehicle.year} {vehicle.make} {vehicle.model}
+                    </p>
+                    {vehicle.nickname && (
+                      <p className="text-sm text-slate-500 dark:text-titanio">{vehicle.nickname}</p>
+                    )}
+                  </div>
+                ))}
+              </div>
+            )}
+          </div>
+        </GlassCard>
+
         {/* Notifications Section */}
         <GlassCard padding="md">
           <div>