fix: default room 'general', cap auto codec at 24k

- Android default room changed from 'android' to 'general'
- Relay choose_profile capped at GOOD (Opus 24k) — studio tiers
  (32k/48k/64k) cause high packet loss on federation paths due to
  larger datagrams exceeding path MTU. Will re-enable after MTU
  discovery is implemented.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

android/app/src/main/java/com/wzp/ui/call/CallViewModel.kt

@@ -138,7 +138,7 @@ class CallViewModel : ViewModel(), WzpCallback {
             ServerEntry("172.16.81.175:4433", "LAN (172.16.81.175)"),
             ServerEntry("193.180.213.68:4433", "Pangolin (IP)"),
         )
-        const val DEFAULT_ROOM = "android"
+        const val DEFAULT_ROOM = "general"
     }
 
     fun setContext(context: Context) {