unregisterCall method
Unregisters a call, removing it from held-calls tracking.
Call this when a call ends (BYE received or local hang-up) to clean up.
Implementation
void unregisterCall(String? callId) {
if (callId == null) return;
_registeredCallIds.remove(callId);
_heldCalls.removeWhere((c) => c.callId == callId);
if (_currentCall?.callId == callId) {
_currentCall = null;
_currentCallController.add(null);
}
_notifyHeldCallsChanged();
}