Backend: - /api/admin/users: GET list, POST create, PUT update, DELETE - Admin users can be added with email, display name, and password - Self-deletion and last-admin deletion are blocked - Admin role auto-assigned on creation Frontend: - AdminUsersTabComponent: list + add/delete admin users - AdminUserService: HTTP client for admin user CRUD - AdminUser interface - 'Admins' tab added to admin dashboard Tests: - 10 new tests for admin user management endpoints - 140 total tests pass (130 original + 10 new)