feat(admin): enhance admin dashboard, user management, and content editor UX

- Dashboard: add stats API with content status distribution, recent notifications,
  and recent content updates; display active users, pending reviews, unread counts
- User management: full CRUD with role assignment, search, pagination, delete dialog
- Notification center: list with unread filter, mark as read, mark all as read,
  pagination, and auto-refresh unread count
- Content editor: form validation (required fields, slug format, blur-triggered
  errors), auto-save with 3s debounce and status indicator, publish confirmation
  dialog, unsaved changes warning on leave
- Admin layout: add navigation links for user management, roles, and notifications
- admin-api: make request() method public for custom API calls
- gitignore: add reports/mutation/ to exclude mutation test output

src/lib/admin-api.ts

@@ -8,7 +8,7 @@ class AdminApiClient {
     return localStorage.getItem('novalon_admin_token');
   }
 
-  private async request<T>(
+  async request<T>(
     path: string,
     options: RequestInit & { encrypt?: boolean } = {},
   ): Promise<T> {