Fixes connecting Immortal to Music Assistant for multi-room audio:
- Music Assistant's server port is now configurable, and defaults to 8095 (MA's standard port). Earlier builds assumed a different port, so a normal Music Assistant setup would report "Can't reach Music Assistant" even when everything else was correct.
- Signing in is now optional. If your Music Assistant doesn't require a login, just enter the server address — no username or password needed. The Sign-in button now also doubles as a connection test, confirming the Portal can reach your server.