* desktop: pick a free port for the call server if 50395 is in use
startServer() bound a hard-coded port (50395); when it was already in use,
NanoWSD threw "BindException: Address already in use: bind" and the call
failed. It now falls back to an OS-assigned free port, and WebRTCController
opens the browser at the actually-bound port (server.listeningPort) -- still
50395 in the normal case, so browser camera/mic permission stays put.
* plans: justify call server port-bind fix
Narasimha-sc