Refactor activation handling and introduce entity system

Added new `ActivationHandler` class for folder initialization.
Added `ProjectService` class for project-related operations.
Added `Ghost.Entities` project with entity management classes.
Added `EngineEditorWindow` for enhanced user interface.

Changed project files to restructure dependencies and remove unused references.
Changed `ProjectRepository` to use asynchronous methods for improved performance.
Changed data binding in `CreateProjectPage.xaml` and `OpenProjectPage.xaml` to use new data models.
Changed `App.xaml.cs` to utilize the new `ActivationHandler` and include additional services.

Removed `IActivationHandler` interface and integrated its functionality into `ActivationHandler`.
Removed `EditorActivationHandler` as its functionality was merged into `ActivationHandler`.

Updated `AssemblyInfo.cs` to include global using directives for entity types.
Updated image assets to reflect visual resource changes.

Ghost.Data/JsonContext.cs

@@ -0,0 +1,10 @@
+using Ghost.Data.Models;
+using System.Text.Json.Serialization;
+
+namespace Ghost.Data;
+
+[JsonSourceGenerationOptions(WriteIndented = true)]
+[JsonSerializable(typeof(TemplateInfo))]
+internal partial class JsonContext : JsonSerializerContext
+{
+}