* Allow Plex port (32400/tcp) through UFW on london-b
Plex needs direct access on port 32400 for remote streaming.
Adds common_ufw_allowed_ports to london-b host_vars.
* Add BitTorrent port (6881) to london-b UFW allowed ports
Port was already manually configured in UFW, bringing it under Ansible management.
These services run on helsinki-a, not london-b. Verified via docker ps
on both hosts. deploy.yml would have managed them on the wrong host.
Fixes PESO-73
