Creates or invites a Partly account, with the request body stating the intent. password: self sign-up, needs no authorization, emails an address-confirmation link. organization_invite_email: partly_staff, or an admin presenting a token scoped to that organization, invites someone into that organization and its groups, each group carrying an is_admin flag; the invitee sets their own credential from the email, or signs in through the IdP when the organization is SSO-required. organization_invite_as_staff: partly_staff attaches a member directly, optionally with a caller-supplied password and an optional email; without an email the user must already be able to sign in, so supply a password, target a user who has one, or invite into an SSO-required organization — which never accepts a password. invite_staff: grants Partly staff scopes and creates a platform-level account with no organization, emailing a set-password link. An address that already has an account is never given a new credential — it is attached, or granted scopes, as it is.