feat: Handle missing Prelude response type

[86667]

• Handle Prelude's Blocked: inavlid_phone_number variant
• Also default when blocked reason is unknown

Before:

ERROR Failed to communicate with SMS provider error=error decoding response body
→ HTTP 500 Internal Server Error

After:

INFO Phone number blocked for reason: InvalidPhoneNumber. prelude id: ...
→ HTTP 403 Forbidden — "Phone number blocked for verification"