[Fixed] Paid forum subscriptions now renew and expire on schedule

We found and fixed an issue with paid private-forum subscriptions not always updating on their billing cycle. A renewing subscription could lose access at the end of its period even though payment had gone through, and a subscription that stopped paying could keep access a little longer than it should. Renewals now extend access correctly, and non-payment or cancellation ends access on schedule. Fixed and deployed to every site.