Fix audio waveform view scene rect and timebase refresh

- AudioWaveformView now uses the video frame rate as its timebase
  (falling back to the default sequence frame rate), preventing the
  enormous scene rect that froze the UI when it previously used the
  audio sample rate.
- Call UpdateSceneRect() after changing the waveform timebase so the
  QGraphicsScene bounds are recomputed immediately.
- Refresh the waveform view's viewer/timebase whenever the waveform
  visibility mode changes, ensuring the correct timebase is applied
  even if the node was connected earlier with a different setting.

app/widget/viewer/audiowaveformview.cpp

@@ -67,11 +67,12 @@ void AudioWaveformView::SetViewer(ViewerOutput *playback)
 		connect(playback_, &ViewerOutput::ConnectedWaveformChanged, viewport(),
 				static_cast<void (QWidget::*)()>(&QWidget::update));
 
-		SetTimebase(playback_->GetVideoParams().frame_rate_as_time_base());
-		if (timebase().isNull()) {
-			SetTimebase(
-				playback_->GetAudioParams().sample_rate_as_time_base());
+		rational tb = playback_->GetVideoParams().frame_rate_as_time_base();
+		if (tb.isNull()) {
+			tb = OLIVE_CONFIG("DefaultSequenceFrameRate").value<rational>().flipped();
 		}
+		SetTimebase(tb);
+		UpdateSceneRect();
 	}
 }
 

app/widget/viewer/viewer.cpp

@@ -826,6 +826,12 @@ void ViewerWidget::UpdateWaveformViewFromMode()
 
 	if (GetConnectedNode()) {
 		GetConnectedNode()->SetWaveformEnabled(waveform_view_->isVisible());
+
+		if (waveform_view_->isVisible()) {
+			waveform_view_->SetViewer(GetConnectedNode());
+		} else {
+			waveform_view_->SetViewer(nullptr);
+		}
 	}
 }