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/admin/api/admin.api.ts

@@ -56,6 +56,23 @@ export interface AuditLogsResponse {
   total: number;
 }
 
+// Admin stats response
+export interface AdminStatsResponse {
+  totalVehicles: number;
+  totalUsers: number;
+}
+
+// User vehicle (admin view)
+export interface AdminUserVehicle {
+  year: number;
+  make: string;
+  model: string;
+}
+
+export interface AdminUserVehiclesResponse {
+  vehicles: AdminUserVehicle[];
+}
+
 // Admin access verification
 export const adminApi = {
   // Verify admin access
@@ -64,6 +81,12 @@ export const adminApi = {
     return response.data;
   },
 
+  // Admin dashboard stats
+  getStats: async (): Promise<AdminStatsResponse> => {
+    const response = await apiClient.get<AdminStatsResponse>('/admin/stats');
+    return response.data;
+  },
+
   // Admin management
   listAdmins: async (): Promise<AdminUser[]> => {
     const response = await apiClient.get<AdminUser[]>('/admin/admins');
@@ -309,6 +332,13 @@ export const adminApi = {
       return response.data;
     },
 
+    getVehicles: async (auth0Sub: string): Promise<AdminUserVehiclesResponse> => {
+      const response = await apiClient.get<AdminUserVehiclesResponse>(
+        `/admin/users/${encodeURIComponent(auth0Sub)}/vehicles`
+      );
+      return response.data;
+    },
+
     updateTier: async (auth0Sub: string, data: UpdateUserTierRequest): Promise<ManagedUser> => {
       const response = await apiClient.patch<ManagedUser>(
         `/admin/users/${encodeURIComponent(auth0Sub)}/tier`,