BestChat V136 - Subscriber background fix

The subscriber pull is now independent from any browser/email page being open.

Recommended cPanel Cron:
*/5 * * * * /usr/local/bin/php /home/bbsasife/bestchat.online/scheduler.php >> /home/bbsasife/bestchat.online/storage/scheduler_cron.log 2>&1

The scheduler loads subscriber_cron.php directly in the same CLI process.
The subscriber cron uses require_once, so it cannot die from a duplicate config include.
It also requeues stale jobs that were left in running state for more than 10 minutes.

For testing only, you can run:
/usr/local/bin/php /home/bbsasife/bestchat.online/subscriber_cron.php

Then check:
storage/scheduler_cron.log
storage/scheduler_heartbeat.log
