Create a SCIM user

Provisions a new Ringover user (RFC 7644 §3.3).

Behavior & limitations:

• This is a real onboarding: an invitation is sent and a license and phone number are consumed from your team.
• A valid email is required: provide a primary emails value or an email-formatted userName, otherwise 400 invalidValue is returned.
• roles[].value must be the numeric profile id (see GET /profiles); a non-numeric value is silently ignored.
• externalId is echoed back but not persisted.