Refund status change notification

Webhook endpoint for receiving refund status change notifications. This is triggered when a refund transitions between states. Use this to track refund progress asynchronously, especially useful when a refund request times out.

Common status transitions:

• PENDING -> COMPLETED: Refund processed successfully
• PENDING -> FAILED: Refund processing failed
• PENDING -> ACTION_REQUIRED: Refund needs partner action (e.g., invalid PIX key — collect a new one from the customer)
• ACTION_REQUIRED -> PENDING: Partner resubmitted corrected data, refund is being retried