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.InternalEditor/Services/StackedNotificationService.cs

@@ -0,0 +1,50 @@
+using CommunityToolkit.WinUI.Behaviors;
+using Microsoft.UI.Xaml.Controls;
+using System;
+
+namespace Ghost.App.Services;
+
+public class StackedNotificationService
+{
+    private InfoBar? _infoBar;
+    private StackedNotificationsBehavior? _notificationQueue;
+
+    internal void SetReference(InfoBar infoBar, StackedNotificationsBehavior notificationQueue)
+    {
+        _infoBar = infoBar;
+        _notificationQueue = notificationQueue;
+    }
+
+    internal void ClearReference()
+    {
+        if (_infoBar != null)
+        {
+            _infoBar.IsOpen = false;
+        }
+        _infoBar = null;
+        _notificationQueue = null;
+    }
+
+    public void ShowNotification(string? message, InfoBarSeverity severity, int duration = 5, string? title = null)
+    {
+        if (string.IsNullOrWhiteSpace(message))
+        {
+            return;
+        }
+
+        var notification = new Notification
+        {
+            Message = message,
+            Severity = severity,
+            Duration = TimeSpan.FromSeconds(duration),
+            Title = title
+        };
+
+        ShowNotification(notification);
+    }
+
+    public void ShowNotification(Notification notification)
+    {
+        _notificationQueue?.Show(notification);
+    }
+}