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/SceneGraph/WorldNode.cs

@@ -0,0 +1,112 @@
+using Ghost.Editor.Serializer;
+using Ghost.Engine.Components;
+using Ghost.Entities;
+using System.Text.Json.Serialization;
+
+namespace Ghost.Editor.SceneGraph;
+
+[JsonConverter(typeof(WorldNodeSerializer))]
+public partial class WorldNode : SceneGraphNode
+{
+    private readonly World _world;
+    private Dictionary<Entity, EntityNode> _entityNodeLookup = new();
+
+    public World World => _world;
+    public Dictionary<Entity, EntityNode> EntityNodeLookup => _entityNodeLookup;
+
+    public override SceneGraphNodeType NodeType => SceneGraphNodeType.Scene;
+
+    public WorldNode(World world, string name)
+    {
+        _world = world;
+        Name = name;
+    }
+
+    internal WorldNode()
+    {
+        _world = World.Create();
+    }
+
+    private void UpdateLookup(Entity key, EntityNode value)
+    {
+        _entityNodeLookup[key] = value;
+        if (value.Children == null)
+        {
+            return;
+        }
+
+        foreach (var child in value.Children)
+        {
+            if (child is EntityNode entityChild)
+            {
+                UpdateLookup(entityChild.Entity, entityChild);
+            }
+        }
+    }
+
+    public override void AddChild(SceneGraphNode child)
+    {
+        if (child is not EntityNode entityNode)
+        {
+            throw new ArgumentException("Child must be of type EntityNode.", nameof(child));
+        }
+
+        base.AddChild(entityNode);
+        UpdateLookup(entityNode.Entity, entityNode);
+    }
+
+    public override bool RemoveChild(SceneGraphNode child)
+    {
+        if (child is not EntityNode entityNode)
+        {
+            throw new ArgumentException("Child must be of type EntityNode.", nameof(child));
+        }
+
+        var result = base.RemoveChild(child);
+        if (result)
+        {
+            _entityNodeLookup.Remove(entityNode.Entity);
+        }
+
+        return result;
+    }
+
+    private EntityNode BuildNodeRecursive(Entity entity, World world)
+    {
+        // TODO: Node serialization.
+        if (!_entityNodeLookup.TryGetValue(entity, out var node))
+        {
+            node = new EntityNode(entity, "New Entity");
+            _entityNodeLookup[entity] = node;
+        }
+
+        var hc = world.EntityManager.GetComponent<Hierarchy>(entity);
+        var child = hc.ValueRO.firstChild;
+
+        while (child != Entity.Invalid)
+        {
+            node.AddChild(BuildNodeRecursive(child, world));
+            var childHC = world.EntityManager.GetComponent<Hierarchy>(child);
+            child = childHC.ValueRO.nextSibling;
+        }
+
+        return node;
+    }
+
+    private void BuildGraph()
+    {
+        foreach (var (entity, hierarchy) in _world.Query<Hierarchy>())
+        {
+            if (hierarchy.ValueRO.parent == Entity.Invalid)
+            {
+                var node = BuildNodeRecursive(entity, _world);
+                AddChild(node);
+            }
+        }
+    }
+
+    public void Load()
+    {
+        BuildGraph();
+    }
+}