Academy LMS <= 4.0.3 - Authenticated (Custom+) Privilege Escalation to add_child REST endpoint

The Academy LMS – AI Course Builder, Quizzes, Certificates & eLearning plugin for WordPress is vulnerable to Privilege Escalation in all versions up to, and including, 4.0.3. This is due to the `add_child()` function calling `add_role('academy_student')` on any existing account resolved from the attacker-supplied `email` parameter before `Store::link()` validates the guardian-ward relationship, and failing to roll back that role write when `Store::link()` returns a `WP_Error`. This makes it possible for authenticated attackers with the `academy_guardian` role or higher to elevate any existing WordPress account — including their own — to the `academy_student` role, gaining `edit_posts` (Contributor-equivalent) capabilities and, when the student file-upload setting is enabled, `upload_files` (Author-equivalent) capabilities not granted to the guardian role. When a guardian supplies their own email address, `email_exists()` resolves to their own user ID, causing `Store::link()` to reject the self-link, but because the `add_role()` call has already executed and is never reversed, the academy_student role grant on their own account persists permanently.