Fix inbound text flow creating blank ghost contacts

When an inbound text arrived without a usable sender phone number, the
CRM was still creating a contact record — but with blank name, email,
and phone. Those “ghost” contacts carried only the default lead-flow
assignments (Team, User, Stage, Lead source: Inbound Text, Assigned
to) and cluttered contact lists.

What’s Fixed

• Contact creation now happens atomically with the phone number save.
  If the phone number can’t be saved, the contact isn’t created
  either — no more orphan records.
• Webhooks with a blank or malformed sender number are now dropped
  (and reported to monitoring) instead of silently generating a ghost
  contact.
• Applies to inbound SMS via SendBlue, Twilio SMS, and Twilio
  Conversations group messages.