program_membership.created

occurs when a new program membership is created in Hang's system

{
  "type": "program_membership.created",
  "id": "webhook_id",
  "webhook_sent_at": 1723058546,
  "program_membership": {
    "id": "program_membership_id",
    "phone": "[phone]",
    "external_user_id": "external_user_id",
    "magic_link": "https://your_subdomain/direct-auth?..."
  }
}