Polar End-to-End: Payments trigger Ghost membership and welcome email

The first full payment-to-membership flow is live. A Polar purchase now reliably creates a Ghost member with the correct plan, labels, and a welcome email, without any manual steps.

• Polar order.paid webhook: Ghost member created automatically with comped plan and PayGlue labels
• Welcome email delivered via Ghost Admin API. Magic link is the recommended default for payment flows
• Email type selector in mapping settings: choose between magic link, confirmation, or no email
• Unsupported event types are silently acknowledged and never stored, keeping the event log clean