Reset the caller back to the FULL new-user onboarding experience.

<br/>Admin-only. Resets the current admin's OWN account (scoped strictly to<br/>current_user(), there is no target-id param, so there is no<br/>cross-user reset path). Two things happen:<br/><br/>1. The funnel row is cleared so whoami reports not-onboarded and the<br/> gate re-runs the two intake questions.<br/>2. The Getting Started baselines are re-captured at the CURRENT asset<br/> counts, so the home-page checklist reads 0/3, and the system behaves<br/> as if the admin has zero avatars without deleting anything.<br/><br/>Non-admins get 403; anonymous callers get 401.