Outbound Webhooks

introduces outbound Webhooks: a tenant can register one or more HTTP endpoints (a Webhook Subscription) and select which events they want pushed to it. When a subscribed event occurs, PanicSafe POSTs a signed JSON payload to the endpoint, with at-least-once delivery, automatic retries with backoff, and a per-delivery audit log so an admin can see what was sent, the response, and replay a failed delivery.