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>

backend/src/features/admin/README.md

@@ -62,14 +62,56 @@ Provides:
 - `admin-guard` plugin - Authorization enforcement (decorator on Fastify)
 - `request.userContext` - Enhanced with `isAdmin`, `adminRecord`
 
-### Phase 2: Admin Management APIs
+### Admin Dashboard Stats
 
-Will provide:
-- `/api/admin/admins` - List all admins (GET)
-- `/api/admin/admins` - Add admin (POST)
-- `/api/admin/admins/:auth0Sub/revoke` - Revoke admin (PATCH)
-- `/api/admin/admins/:auth0Sub/reinstate` - Reinstate admin (PATCH)
-- `/api/admin/audit-logs` - View audit trail (GET)
+Provides admin dashboard statistics:
+
+- `GET /api/admin/stats` - Get total users and vehicles counts
+
+**Response:**
+```json
+{
+  "totalUsers": 150,
+  "totalVehicles": 287
+}
+```
+
+### User Management APIs
+
+Provides:
+- `GET /api/admin/users` - List all users with pagination/filters
+- `GET /api/admin/users/:auth0Sub` - Get single user details
+- `GET /api/admin/users/:auth0Sub/vehicles` - Get user's vehicles (admin view)
+- `PATCH /api/admin/users/:auth0Sub/tier` - Update subscription tier
+- `PATCH /api/admin/users/:auth0Sub/deactivate` - Deactivate user
+- `PATCH /api/admin/users/:auth0Sub/reactivate` - Reactivate user
+- `PATCH /api/admin/users/:auth0Sub/profile` - Update user profile
+- `PATCH /api/admin/users/:auth0Sub/promote` - Promote to admin
+- `DELETE /api/admin/users/:auth0Sub` - Hard delete user (GDPR)
+
+**User Vehicles Endpoint:**
+```
+GET /api/admin/users/:auth0Sub/vehicles
+```
+
+Returns minimal vehicle data for privacy (Year/Make/Model only):
+```json
+{
+  "vehicles": [
+    { "year": 2022, "make": "Toyota", "model": "Camry" },
+    { "year": 2020, "make": "Honda", "model": "Civic" }
+  ]
+}
+```
+
+### Admin Management APIs
+
+Provides:
+- `GET /api/admin/admins` - List all admins
+- `POST /api/admin/admins` - Add admin
+- `PATCH /api/admin/admins/:auth0Sub/revoke` - Revoke admin
+- `PATCH /api/admin/admins/:auth0Sub/reinstate` - Reinstate admin
+- `GET /api/admin/audit-logs` - View audit trail
 
 ### Phase 3: Platform Catalog CRUD (COMPLETED)