Replace three-button cluster with a single context-aware primary button

Button follows the user journey: 'Connect to YouTube' (not signed in)
-> 'Go Live' (connected, idle) -> 'Stop Stream' (live).

MainWindow.xaml

@@ -119,38 +119,10 @@
                     </StackPanel>
                 </Border>
 
-                <!-- Stream Controls -->
+                <!-- Primary action: single button, adapts to state -->
                 <StackPanel Grid.Column="3" Orientation="Horizontal" VerticalAlignment="Center">
-
-                    <!-- YouTube connection status light + button -->
-                    <Border Background="#0f3460" CornerRadius="4" Padding="8,6" Margin="0,0,12,0"
-                            VerticalAlignment="Center" ToolTip="YouTube connection status">
-                        <StackPanel Orientation="Horizontal">
-                            <Ellipse Width="10" Height="10" Margin="0,0,8,0" VerticalAlignment="Center">
-                                <Ellipse.Style>
-                                    <Style TargetType="Ellipse">
-                                        <Setter Property="Fill" Value="#555"/>
-                                        <Style.Triggers>
-                                            <DataTrigger Binding="{Binding IsYouTubeConnected}" Value="True">
-                                                <Setter Property="Fill" Value="#00ff00"/>
-                                            </DataTrigger>
-                                        </Style.Triggers>
-                                    </Style>
-                                </Ellipse.Style>
-                            </Ellipse>
-                            <Button Content="YouTube" Style="{StaticResource YtButtonSecondary}"
-                                    Background="Transparent" Padding="0"
-                                    Command="{Binding ConnectYouTubeCommand}"
-                                    ToolTip="Sign in to YouTube (optional)"/>
-                        </StackPanel>
-                    </Border>
-
-                    <Button Content="Go Live" Style="{StaticResource YtButton}"
-                            Command="{Binding StartStreamCommand}"
-                            Visibility="{Binding IsOffline, Converter={StaticResource BoolToVis}}"/>
-                    <Button Content="Stop Stream" Style="{StaticResource YtButton}"
-                            Background="#333" Command="{Binding StopStreamCommand}"
-                            Visibility="{Binding IsLive, Converter={StaticResource BoolToVis}}"/>
+                    <Button Content="{Binding PrimaryButtonText}" Style="{StaticResource YtButton}"
+                            Command="{Binding PrimaryCommand}"/>
                 </StackPanel>
             </Grid>
         </Border>

ViewModels/MainViewModel.cs

@@ -38,6 +38,7 @@ public class MainViewModel : ViewModelBase
                 OnPropertyChanged(nameof(IsOffline));
                 OnPropertyChanged(nameof(IsLive));
                 OnPropertyChanged(nameof(StatusDisplay));
+                OnPropertyChanged(nameof(PrimaryButtonText));
             }
         }
     }
@@ -66,7 +67,11 @@ public class MainViewModel : ViewModelBase
     public bool IsYouTubeConnected
     {
         get => _isYouTubeConnected;
-        set => SetProperty(ref _isYouTubeConnected, value);
+        set
+        {
+            if (SetProperty(ref _isYouTubeConnected, value))
+                OnPropertyChanged(nameof(PrimaryButtonText));
+        }
     }
 
     public string StatusDisplay => StreamStatus switch
@@ -78,12 +83,20 @@ public class MainViewModel : ViewModelBase
         _ => "UNKNOWN"
     };
 
+    /// <summary>
+    /// Single, context-aware primary button. Follows the user's journey:
+    /// not connected → connect, connected+idle → go live, live → stop.
+    /// </summary>
+    public string PrimaryButtonText => !IsYouTubeConnected
+        ? "Connect to YouTube"
+        : IsLive
+            ? "Stop Stream"
+            : "Go Live";
+
     // Commands
     public ICommand AddSceneCommand { get; }
     public ICommand RemoveSceneCommand { get; }
-    public ICommand StartStreamCommand { get; }
-    public ICommand StopStreamCommand { get; }
-    public ICommand ConnectYouTubeCommand { get; }
+    public ICommand PrimaryCommand { get; }
 
     public MainViewModel()
     {
@@ -95,9 +108,7 @@ public class MainViewModel : ViewModelBase
 
         AddSceneCommand = new RelayCommand(_ => AddScene());
         RemoveSceneCommand = new RelayCommand(scene => RemoveScene(scene as Scene));
-        StartStreamCommand = new RelayCommand(_ => StartStream(), _ => StreamStatus == StreamStatus.Offline);
-        StopStreamCommand = new RelayCommand(_ => StopStream(), _ => StreamStatus == StreamStatus.Streaming);
-        ConnectYouTubeCommand = new RelayCommand(_ => ConnectYouTube());
+        PrimaryCommand = new RelayCommand(_ => PrimaryAction());
 
         // Start with a default scene
         AddScene("Scene 1");
@@ -131,19 +142,16 @@ public class MainViewModel : ViewModelBase
     private async void StartStream()
     {
         StreamStatus = StreamStatus.Connecting;
-        OnPropertyChanged(nameof(StatusDisplay));
 
         // TODO: Initialize capture pipeline, encode, and push to RTMP
         // For now, simulate connection
         await Task.Delay(500);
         StreamStatus = StreamStatus.Streaming;
-        OnPropertyChanged(nameof(StatusDisplay));
     }
 
     private void StopStream()
     {
         StreamStatus = StreamStatus.Offline;
-        OnPropertyChanged(nameof(StatusDisplay));
     }
 
     private void ConnectYouTube()
@@ -152,4 +160,14 @@ public class MainViewModel : ViewModelBase
         // For now, this is a stub
         IsYouTubeConnected = false;
     }
+
+    private void PrimaryAction()
+    {
+        if (!IsYouTubeConnected)
+            ConnectYouTube();
+        else if (IsLive)
+            StopStream();
+        else
+            StartStream();
+    }
 }