feat: improve collaboration rooms (#1338)

README.md

@@ -354,6 +354,12 @@ networks:
     driver: bridge
 ```
 
+For multiple Termix backend instances, set the same `REDIS_URL` and optional
+`TERMIX_REDIS_PREFIX` on every instance. Redis synchronizes collaboration room
+presence, control requests, controller state, and events; keep WebSocket session
+affinity enabled because live SSH and remote desktop transports remain attached
+to the backend instance that opened them. A single instance needs no Redis.
+
 ### Command Line Interface
 
 Termix also has a CLI, so you can manage your servers from a terminal and use Termix in your own scripts.