Default PaperTiger.WebhookDelivery.Adapter — performs the HTTP POST
itself using Req. This is the historical PaperTiger behavior and the
adapter in effect when :webhook_delivery_adapter is not configured.
- 2xx response →
{:ok, %Response{status: code, body: body}}(terminal success; PaperTiger records the body on the delivery attempt). - non-2xx response →
{:error, {:http_status, code}}(PaperTiger retries). - transport error / timeout →
{:error, reason}(PaperTiger retries).