Initial scaffold: ytLive C# WPF project

- MVVM architecture (Models, ViewModels, Views, Services, Helpers)
- Models: Scene, Source, StreamConfig, StreamHealth, YouTubeChannel, ChatMessage
- Services: YouTubeAuthService (OAuth2), YouTubeStreamService (broadcasts/stream health),
  YouTubeChatService (live chat polling)
- ViewModels: MainViewModel with scene management, stream controls, chat
- MainWindow with dark theme: scene/source panel, preview area, chat panel, status bar
- Version roadmap: v0.1 (scenes, RTMP, OAuth2, chat, health) -> 1.0

Helpers/ViewModelBase.cs

@@ -0,0 +1,23 @@
+using System.ComponentModel;
+using System.Runtime.CompilerServices;
+
+namespace ytLive.Helpers;
+
+public abstract class ViewModelBase : INotifyPropertyChanged
+{
+    public event PropertyChangedEventHandler? PropertyChanged;
+
+    protected bool SetProperty<T>(ref T field, T value, [CallerMemberName] string? propertyName = null)
+    {
+        if (EqualityComparer<T>.Default.Equals(field, value))
+            return false;
+        field = value;
+        OnPropertyChanged(propertyName);
+        return true;
+    }
+
+    protected void OnPropertyChanged([CallerMemberName] string? propertyName = null)
+    {
+        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
+    }
+}