Companion relay

1. Double-click run.bat, or use COMPANION-SHELL.txt for the Companion button.
2. Pick Studio A (sender) or Studio B (receiver) in the window
3. Studio A receives RossTalk directly on port 7788 and sends it to Railway.
   Point the RossTalk client at the Studio A PC.
   Commands: CC PREVIEW 1, CC PROGRAM 1, CC CUT, CC MIXAUTO
   Studio B must be the receiver. It reads Railway and fires the ATEM.
4. See COMPANION-RELAY.md
   Companion A POSTs http://127.0.0.1:8791/send
   Companion B needs HTTP API :8000 and/or OSC :12321
