post
https://api.qfp.quantnetwork.net/api/auth/activate
Collapses login-then-challenge into a single request: the temporary
password from the invitation email authenticates, and the chosen
password answers the NEW_PASSWORD_REQUIRED challenge that comes
back. Anything but that challenge (tokens included, meaning the
temporary password was already replaced) is 401 Invalid credentials.
On success the platform row is set to ACTIVE, on the same terms as
POST /api/auth/new-password, and the temporary password is spent.

