Added reference docs for the embed-based 1-Click Signup flow:

• POST /private/v1/one-click/sessions — mint a single-use session key for the 1-Click Signup embed
• POST /private/v1/users/one-click — redeem the identity the embed collected and create the user

This is the modal-based counterpart to the server-to-server 1-Click API — see Verified 1-Click API (server-to-server) if you'd rather build your own UI instead of embedding ProphetX's.