refactor(admin): migrate administration list to new architecture
- Add StaffListController (GET /admin/staff) backed by GetStaffListUseCase + StaffListDTO/StaffGroupDTO
- Add StaffRepositoryInterface + EloquentStaffRepository and AdminUserRowMapper (reuses Johncms\Users\User)
- Remove legacy includes/adminlist.php and its $actions entry; point both sidebars to /admin/staff
- AdminAccessMiddleware now returns a sidebar-less 403 page for insufficient rights instead of pageNotFound()
- Add system::error/403 templates to admin (guest layout) and default themes
- Fix RenderEngineFactory/Assets isAdmin() to match bare /admin (no trailing slash) and ignore query string
- Add StaffRepositoryInterface + EloquentStaffRepository and AdminUserRowMapper (reuses Johncms\Users\User)
- Remove legacy includes/adminlist.php and its $actions entry; point both sidebars to /admin/staff
- AdminAccessMiddleware now returns a sidebar-less 403 page for insufficient rights instead of pageNotFound()
- Add system::error/403 templates to admin (guest layout) and default themes
- Fix RenderEngineFactory/Assets isAdmin() to match bare /admin (no trailing slash) and ignore query string