Kill stringly-typed command tokens: Add Source menu passes SourceType enum via x:Static CommandParameter (typos break the build, not silently add an Image); webcam gets its own AddWebcamCommand; AddSource keeps Enum.TryParse fallback; docs updated (65 tests passing)

ViewModels/MainViewModel.cs

@@ -525,6 +525,7 @@ public class MainViewModel : ViewModelBase
     public ICommand RemoveSceneCommand { get; }
     public ICommand ToggleSceneVisibilityCommand { get; }
     public ICommand AddSourceCommand { get; }
+    public ICommand AddWebcamCommand { get; }
     public ICommand AddImageCommand { get; }
     public ICommand RemoveSourceCommand { get; }
     public ICommand ChangeWebcamCommand { get; }
@@ -577,7 +578,8 @@ public class MainViewModel : ViewModelBase
         EditSceneCommand = new RelayCommand(scene => BeginEditScene(scene as Scene));
         RemoveSceneCommand = new RelayCommand(scene => RemoveScene(scene as Scene));
         ToggleSceneVisibilityCommand = new RelayCommand(scene => ToggleSceneVisibility(scene as Scene));
-        AddSourceCommand = new RelayCommand(type => AddSource(type as string));
+        AddSourceCommand = new RelayCommand(parameter => AddSource(parameter));
+        AddWebcamCommand = new RelayCommand(_ => _ = AddWebcamToActiveSceneAsync());
         AddImageCommand = new RelayCommand(_ => AddImage());
         RemoveSourceCommand = new RelayCommand(element => RemoveElement(element as SceneElement));
         ChangeWebcamCommand = new RelayCommand(_ => _ = ChangeWebcamAsync(), _ => CanChangeWebcam);
@@ -1060,25 +1062,14 @@ public class MainViewModel : ViewModelBase
             ActiveScene = Scenes.FirstOrDefault();
     }
 
-    private void AddSource(string? type)
+    private void AddSource(object? parameter)
     {
         var scene = ActiveScene;
         if (scene == null) return;
 
-        if (string.Equals(type, "webcam", StringComparison.OrdinalIgnoreCase))
-        {
-            _ = AddWebcamToActiveSceneAsync();
-            return;
-        }
-
-        var sourceType = type?.ToLowerInvariant() switch
-        {
-            "screen" => SourceType.DisplayCapture,
-            "window" => SourceType.WindowCapture,
-            "background" => SourceType.Background,
-            "text" => SourceType.TextOverlay,
-            _ => SourceType.Image,
-        };
+        var sourceType = parameter is SourceType typed
+            ? typed
+            : Enum.TryParse<SourceType>(parameter?.ToString(), true, out var parsed) ? parsed : SourceType.Image;
         var baseName = sourceType switch
         {
             SourceType.DisplayCapture => "Screen",