Unlink the Auth0 account from the current Firebase user
Remove the linked account record for the authenticated Firebase user.
Authenticates via the standard Authorization: Bearer <firebase_id_token> header.
Returns 404 if no linked account exists, mirroring the GET rather than
reporting success for a link that was never there.
Unlinking stops the association going forward. It does not delete the memories that were shared while the link existed.
DELETE
https://truememory-auth.mvstg.com/auth/link_mv_account