Webhooks: real-time event notifications

You can now receive real-time webhooks for transaction, recovery, and refund lifecycle events. Deliveries are HMAC-signed and automatically retried, with durable buffering if your endpoint is down. From the Client Portal you can register endpoints, rotate signing secrets, send test deliveries to validate an endpoint, and browse full event and delivery history. Documentation covers consumption patterns, idempotency, and error handling.