Refactor project from Ghost.App to Ghost.Editor

Changed the project structure to reflect a shift from `Ghost.App` to `Ghost.Editor`, updating namespaces and class names throughout.

Changed the application class in `App.xaml` and `App.xaml.cs` from `GhostApplication` to `EditorApplication`.

Changed several service interfaces to reside under `Ghost.Editor.Services.Contracts`, including `IInspectorService`, `INotificationService`, and `IProgressService`.

Added `InspectorView` and `InspectorViewModel` classes to manage inspector functionality.

Added `NavigationTabView` and `NavigationTabPage` classes to facilitate navigation within the editor.

Enhanced `WorldNode` and `EntityNode` classes to support scene graph functionality, including serialization and entity management.

Updated the project file `Ghost.Editor.csproj` to reflect the new structure and removed old references.

Modified the solution file `GhostEngine.sln` to remove references to `Ghost.App` and include `Ghost.Editor`.

Updated unit tests to align with the new namespaces and project structure.

Ghost.App/Core/SceneGraph/SceneGraphNode.cs

@@ -0,0 +1,54 @@
+using CommunityToolkit.Mvvm.ComponentModel;
+using System.Collections.ObjectModel;
+
+namespace Ghost.Editor.Core.SceneGraph;
+
+public enum SceneGraphNodeType
+{
+    Scene,
+    Entity,
+}
+
+public abstract partial class SceneGraphNode : ObservableObject
+{
+    public ObservableCollection<SceneGraphNode>? Children
+    {
+        get;
+        private set;
+    }
+
+    [ObservableProperty]
+    public partial string Name
+    {
+        get;
+        set;
+    }
+
+    public abstract SceneGraphNodeType NodeType
+    {
+        get;
+    }
+
+    public int ChildCount => Children?.Count ?? 0;
+
+    public virtual void AddChild(SceneGraphNode child)
+    {
+        Children ??= new();
+        Children.Add(child);
+    }
+
+    public virtual bool RemoveChild(SceneGraphNode child)
+    {
+        return Children?.Remove(child) ?? false;
+    }
+
+    public SceneGraphNode GetChild(int index)
+    {
+        if (Children == null || index < 0 || index >= Children.Count)
+        {
+            throw new ArgumentOutOfRangeException(nameof(index), "Index is out of range.");
+        }
+
+        return Children[index];
+    }
+}