Refactor project structure and enhance functionality

Added `InternalsVisibleTo` attribute for "Ghost.Editor" in `AssemblyInfo.cs`.
Added a binary file `Empty.zip` to the project.
Added a new `ProjectMetadata` class in `ProjectMetadata.cs`.
Added new states and interfaces for managing application states in `EditorState.cs`, `LandingState.cs`, and `IAppState.cs`.
Added a notification service in `INotificationService.cs` and `StackedNotificationService.cs`.
Added new XAML files for UI components, including `InspectorView.xaml` and `InternalControls.xaml`.

Changed the `ProjectInfo` class in `ProjectInfo.cs` to include a `MetadataPath` property instead of `Path` and `EngineVersion`.
Changed the `TemplateInfo` class in `TemplateInfo.cs` to use a struct instead of a class for `TemplateData`.
Changed the `ProjectService` class to use the new `ProjectRepository` for managing project data.

Removed several using directives and the entire `ProjectRepository` class from `ProjectRepository.cs`, replacing it with a new implementation.
Removed old methods and properties in `EntityManager` and `World` classes to improve entity management and component handling.

Updated the `Ghost.Data.csproj` file to include the new `Empty.zip` file as a content item.
Updated the `ProjectRepository` class to manage project data using SQLite.
Updated various XAML files to include new styles and controls, improving the overall UI design.
Updated the `CreateProjectViewModel` to include a notification service and handle project creation logic.
Updated the test project to include references to the new `Ghost.Graphics` project and modified test cases to align with the new structure.

Ghost.Data/Models/ProjectInfo.cs

@@ -2,7 +2,7 @@
 
 namespace Ghost.Data.Models;
 
-public class ProjectInfo
+internal class ProjectInfo
 {
     [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
     public int ID
@@ -15,17 +15,7 @@ public class ProjectInfo
         get; set;
     }
 
-    public required string Path
-    {
-        get; set;
-    }
-
-    public required Version EngineVersion
-    {
-        get; set;
-    }
-
-    public required DateTime LastOpened
+    public required string MetadataPath
     {
         get; set;
     }

Ghost.Data/Models/ProjectMetadata.cs

@@ -0,0 +1,51 @@
+namespace Ghost.Data.Models;
+
+public class ProjectMetadata
+{
+    public const string PROJECT_EXTENSION = "ghostproj";
+
+    public Guid ID
+    {
+        get; set;
+    }
+
+    public string Name
+    {
+        get; set;
+    }
+
+    public Version EngineVersion
+    {
+        get; set;
+    }
+
+    public DateTime CreatedAt
+    {
+        get; set;
+    }
+
+    public DateTime LastOpened
+    {
+        get; set;
+    }
+
+    public ProjectMetadata(string name, Version engineVersion)
+    {
+        ID = Guid.NewGuid();
+        Name = name;
+        EngineVersion = engineVersion;
+        CreatedAt = DateTime.UtcNow;
+        LastOpened = DateTime.UtcNow;
+    }
+
+    // Parameterless constructor for deserialization
+    public ProjectMetadata()
+    {
+    }
+}
+
+public readonly struct ProjectMetadataInfo(string path, ProjectMetadata metadata)
+{
+    public readonly string Path => path;
+    public readonly ProjectMetadata Metadata => metadata;
+}

Ghost.Data/Models/Result.cs

@@ -0,0 +1,53 @@
+namespace Ghost.Data.Models;
+
+public readonly struct Result
+{
+    public readonly bool success;
+
+    public readonly string? message;
+
+    public Result(bool success, string? message = null)
+    {
+        this.success = success;
+        this.message = message;
+    }
+
+    public static Result OK()
+    {
+        return new Result(true);
+    }
+
+    public static Result Error(string? message)
+    {
+        return new Result(false, message);
+    }
+
+    public override string ToString() => success ? "OK" : $"Error: {message}";
+}
+
+public readonly struct Result<T>
+{
+    public readonly bool success;
+    public readonly T? data;
+
+    public readonly string? message;
+
+    public Result(bool success, T? data, string? message = null)
+    {
+        this.success = success;
+        this.data = data;
+        this.message = message;
+    }
+
+    public static Result<T> OK(T data)
+    {
+        return new Result<T>(true, data);
+    }
+
+    public static Result<T> Error(string? message)
+    {
+        return new Result<T>(false, default, message);
+    }
+
+    public override string ToString() => success ? $"OK: {data}" : $"Error: {message}";
+}

Ghost.Data/Models/TemplateInfo.cs

@@ -23,21 +23,21 @@ public class TemplateInfo
     }
 }
 
-public class TemplateData(string templatePath, TemplateInfo info)
+public struct TemplateData(string templatePath, TemplateInfo info)
 {
     private const string _ICON_NAME = "icon.png";
     private const string _PREVIEW_NAME = "preview.png";
 
     public string directory = Path.GetDirectoryName(templatePath)!;
 
-    public TemplateInfo Info => info;
+    public readonly TemplateInfo Info => info;
 
-    public Uri GetIconURI()
+    public readonly Uri GetIconURI()
     {
         return new Uri(Path.Combine(directory, _ICON_NAME));
     }
 
-    public Uri GetPreviewURI()
+    public readonly Uri GetPreviewURI()
     {
         return new Uri(Path.Combine(directory, _PREVIEW_NAME));
     }