Refactor project structure and enhance functionality

Changed the project namespace from `Ghost.Editor` to `Ghost.App` across multiple files.
Changed the `InternalsVisibleTo` attribute in `AssemblyInfo.cs` to include `Ghost.App`.
Changed the `ProjectRepository` class to add new asynchronous methods for retrieving projects by ID, name, and metadata path.
Changed the `ProjectService` class to utilize the new asynchronous project loading methods.
Changed the `SceneGraph` classes to improve node management and serialization.
Changed the `EntityManager` class to enhance entity management with new component handling methods.
Added new test classes, `EntityTest` and `SerializationTest`, to ensure reliability in entity and serialization systems.
Added the `Ghost.App` project file to establish a modular project structure.
Added the `Ghost.Generator` project for automated component serialization code generation.
Updated UI components to reflect the new namespace for proper functionality.

Ghost.Editor/View/Pages/EngineEditor/HierarchyPage.xaml.cs

@@ -1,57 +0,0 @@
-using Ghost.Editor.Infrastructures.SceneGraph;
-using Ghost.Editor.ViewModels.Pages.EngineEditor;
-using Microsoft.UI.Xaml;
-using Microsoft.UI.Xaml.Controls;
-
-// To learn more about WinUI, the WinUI project structure,
-// and more about our project templates, see: http://aka.ms/winui-project-info.
-
-namespace Ghost.Editor.View.Pages.EngineEditor;
-/// <summary>
-/// An empty page that can be used on its own or navigated to within a Frame.
-/// </summary>
-internal sealed partial class HierarchyPage : Page
-{
-    public HierarchyViewModel ViewModel
-    {
-        get;
-    }
-
-    public HierarchyPage()
-    {
-        ViewModel = App.GetService<HierarchyViewModel>();
-
-        InitializeComponent();
-    }
-}
-
-internal partial class HierarchyTemplateSector : DataTemplateSelector
-{
-    public DataTemplate? SceneTemplate
-    {
-        get;
-        set;
-    }
-
-    public DataTemplate? EntityTemplate
-    {
-        get;
-        set;
-    }
-
-    protected override DataTemplate SelectTemplateCore(object item)
-    {
-        if (SceneTemplate == null || EntityTemplate == null)
-        {
-            return base.SelectTemplateCore(item);
-        }
-
-        var node = (SceneGraphNode)item;
-        return node.Type switch
-        {
-            SceneGraphNode.NodeType.Scene => SceneTemplate,
-            SceneGraphNode.NodeType.Entity => EntityTemplate,
-            _ => base.SelectTemplateCore(item)
-        };
-    }
-}