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/Infrastructures/AppState/AppStateMachine.cs

@@ -0,0 +1,38 @@
+using System;
+using System.Collections.Generic;
+using System.Threading.Tasks;
+
+namespace Ghost.App.Infrastructures.AppState;
+
+internal class AppStateMachine
+{
+    private Dictionary<StateKey, Lazy<IAppState>> s_states = new();
+    private IAppState? s_current;
+
+    public void RegisterState(StateKey key, Func<IAppState> stateFactory)
+    {
+        s_states[key] = new(stateFactory);
+    }
+
+    public async Task TransitionToAsync(StateKey stateKey, object? parameter = null)
+    {
+        var previous = s_current;
+        var next = s_states[stateKey].Value;
+
+        if (previous != null)
+        {
+            await previous.OnExitingAsync();
+        }
+
+        await next.OnEnteringAsync(parameter);
+
+        if (previous != null)
+        {
+            await previous.OnExitedAsync();
+        }
+
+        await next.OnEnteredAsync(parameter);
+
+        s_current = next;
+    }
+}