Gives Traitor AIs the Syndicate Channel!

This PR is intended to support #5283 .
- Traitor AIs, when set as a traitor, will be given a new internal radio
calibrated to hear and transmit to the encrypted syndicate frequency.

Since traitors can buy a headset key for getting the Syndicate Channel,
Traitor AIs can get one too, as they cannot purchase their own TC items.
Can't you just do radio.make_syndie()?