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

App.xaml

@@ -0,0 +1,9 @@
+<Application x:Class="ytLive.App"
+             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:local="clr-namespace:ytLive"
+             StartupUri="MainWindow.xaml">
+    <Application.Resources>
+         
+    </Application.Resources>
+</Application>