Fix duplicate subscription.activated Stripe webhook events on reactivation

Previously, reactivating a Stripe or external subscription would fire both subscription.activated and subscription.reactivated events. The subscription.activated event is now sent only on the first activation — reactivations (from canceled or churned) fire only the subscription.reactivated event. This aligns Stripe and external order behavior with PAI orders and removes the need to deduplicate these events in your integration, which, in some cases, may not be easily feasible or may be error-prone.