feat: implement scene graph system with ECS hierarchy support

Add hierarchical scene graph for editor with TreeView UI, runtime
HierarchyUtility for parent/child linked-list management, and
incremental sync between editor world and scene graph nodes.

- SceneGraphNode/SceneNode/EntityNode with World, Scene, Entity refs
- SceneGraphBuilder — construct tree from ECS World queries
- HierarchyUtility — SetParent, RemoveParent, IsAncestor, cascade destroy
- EditorWorldService + SceneGraphSyncService — editor world lifecycle & incremental sync
- Hierarchy.xaml — TreeView with DataTemplate + SceneGraphTemplateSelector
- 25 unit tests covering hierarchy ops and scene graph building

src/Editor/Ghost.Editor/Ghost.Editor.csproj

@@ -38,10 +38,10 @@
     <PackageReference Include="CommunityToolkit.WinUI.Controls.Primitives" Version="8.2.251219" />
     <PackageReference Include="CommunityToolkit.WinUI.Controls.Sizers" Version="8.2.251219" />
     <PackageReference Include="CommunityToolkit.WinUI.Controls.TabbedCommandBar" Version="8.2.251219" />
-    <PackageReference Include="Microsoft.Extensions.Hosting" Version="10.0.6" />
+    <PackageReference Include="Microsoft.Extensions.Hosting" Version="10.0.7" />
     <PackageReference Include="Microsoft.Windows.CsWinRT" Version="2.2.0" />
-    <PackageReference Include="Microsoft.Windows.SDK.BuildTools" Version="10.0.28000.1721" />
-    <PackageReference Include="Microsoft.WindowsAppSDK" Version="1.8.260317003" />
+    <PackageReference Include="Microsoft.Windows.SDK.BuildTools" Version="10.0.28000.1839" />
+    <PackageReference Include="Microsoft.WindowsAppSDK" Version="2.0.1" />
     <PackageReference Include="WinUIEx" Version="2.9.0" />
   </ItemGroup>
   <ItemGroup>

src/Editor/Ghost.Editor/Views/Controls/Hierarchy.xaml

@@ -5,9 +5,40 @@
     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
     xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
     xmlns:local="using:Ghost.Editor.Views.Controls"
+    xmlns:sg="using:Ghost.Editor.Core.SceneGraph"
     xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
     mc:Ignorable="d">
 
+    <UserControl.Resources>
+        <local:SceneGraphTemplateSelector
+            x:Key="SceneGraphTemplateSelector"
+            SceneNodeTemplate="{StaticResource SceneNodeTemplate}"
+            EntityNodeTemplate="{StaticResource EntityNodeTemplate}" />
+
+        <DataTemplate x:Key="SceneNodeTemplate" x:DataType="sg:SceneNode">
+            <TreeViewItem
+                AutomationProperties.Name="{x:Bind Name, Mode=OneWay}"
+                IsExpanded="True"
+                ItemsSource="{x:Bind Children, Mode=OneWay}">
+                <StackPanel Orientation="Horizontal">
+                    <FontIcon FontSize="14" Glyph="&#xF156;" />
+                    <TextBlock Margin="10,0,0,0" Text="{x:Bind Name, Mode=OneWay}" />
+                </StackPanel>
+            </TreeViewItem>
+        </DataTemplate>
+
+        <DataTemplate x:Key="EntityNodeTemplate" x:DataType="sg:EntityNode">
+            <TreeViewItem
+                AutomationProperties.Name="{x:Bind Name, Mode=OneWay}"
+                ItemsSource="{x:Bind Children, Mode=OneWay}">
+                <StackPanel Orientation="Horizontal">
+                    <FontIcon FontSize="14" Glyph="&#xF158;" />
+                    <TextBlock Margin="5,0,0,0" Text="{x:Bind Name, Mode=OneWay}" />
+                </StackPanel>
+            </TreeViewItem>
+        </DataTemplate>
+    </UserControl.Resources>
+
     <Grid>
         <Grid.RowDefinitions>
             <RowDefinition Height="Auto" />
@@ -50,19 +81,17 @@
                     Margin="0,0,4,0"
                     FontSize="{StaticResource ToolbarFontIconFontSize}"
                     Glyph="&#xE721;" />
-                <TextBox Grid.Column="1" PlaceholderText="Sreach item..." />
+                <TextBox Grid.Column="1" PlaceholderText="Search item..." />
             </Grid>
 
             <Border Margin="-8,8,-4,-4" Style="{StaticResource HorizontalStrongDivider}" />
         </StackPanel>
 
-        <ListView Grid.Row="1" Padding="4,2,0,2">
-            <ListViewItem Content="Test" />
-            <ListViewItem Content="Test" />
-            <ListViewItem Content="Test" />
-            <ListViewItem Content="Test" />
-            <ListViewItem Content="Test" />
-            <ListViewItem Content="Test" />
-        </ListView>
+        <TreeView
+            x:Name="SceneTreeView"
+            Grid.Row="1"
+            Padding="4,2,0,2"
+            ItemTemplateSelector="{StaticResource SceneGraphTemplateSelector}"
+            SelectionMode="Single" />
     </Grid>
 </UserControl>

src/Editor/Ghost.Editor/Views/Controls/Hierarchy.xaml.cs

@@ -1,14 +1,62 @@
+using Ghost.Editor.Core.Contracts;
+using Ghost.Editor.Core.Services;
+using Microsoft.UI.Dispatching;
 using Microsoft.UI.Xaml.Controls;
 
-// To learn more about WinUI, the WinUI project structure,
-// and more about our project templates, see: http://aka.ms/winui-project-info.
-
 namespace Ghost.Editor.Views.Controls;
 
 public sealed partial class Hierarchy : UserControl
 {
+    private readonly SceneGraphSyncService _syncService;
+    private readonly IInspectorService _inspectorService;
+    private readonly EditorWorldService _worldService;
+    private DispatcherQueueTimer? _syncTimer;
+
     public Hierarchy()
     {
         InitializeComponent();
+
+        _syncService = App.GetService<SceneGraphSyncService>();
+        _inspectorService = App.GetService<IInspectorService>();
+        _worldService = App.GetService<EditorWorldService>();
+
+        SceneTreeView.ItemsSource = _worldService.RootNodes;
+
+        SceneTreeView.ItemInvoked += OnTreeViewItemInvoked;
+        SceneTreeView.SelectionChanged += OnTreeViewSelectionChanged;
+
+        _syncTimer = DispatcherQueue.GetForCurrentThread().CreateTimer();
+        _syncTimer.Interval = TimeSpan.FromMilliseconds(100);
+        _syncTimer.Tick += OnSyncTick;
+        _syncTimer.Start();
+
+        Unloaded += OnUnloaded;
+    }
+
+    private void OnSyncTick(DispatcherQueueTimer sender, object args)
+    {
+        if (_syncService.Tick())
+        {
+        }
+    }
+
+    private void OnTreeViewItemInvoked(TreeView sender, TreeViewItemInvokedEventArgs args)
+    {
+        if (args.InvokedItem is IInspectable inspectable)
+        {
+            _inspectorService.SetSelected(inspectable, this);
+        }
+    }
+
+    private void OnTreeViewSelectionChanged(object sender, TreeViewSelectionChangedEventArgs args)
+    {
+    }
+
+    private void OnUnloaded(object sender, Microsoft.UI.Xaml.RoutedEventArgs e)
+    {
+        _syncTimer?.Stop();
+        SceneTreeView.ItemInvoked -= OnTreeViewItemInvoked;
+        SceneTreeView.SelectionChanged -= OnTreeViewSelectionChanged;
+        Unloaded -= OnUnloaded;
     }
 }

src/Editor/Ghost.Editor/Views/Controls/SceneGraphTemplateSelector.cs

@@ -0,0 +1,35 @@
+using Ghost.Editor.Core.SceneGraph;
+using Microsoft.UI.Xaml;
+using Microsoft.UI.Xaml.Controls;
+
+namespace Ghost.Editor.Views.Controls;
+
+public partial class SceneGraphTemplateSelector : DataTemplateSelector
+{
+    public DataTemplate? SceneNodeTemplate
+    {
+        get; set;
+    }
+
+    public DataTemplate? EntityNodeTemplate
+    {
+        get; set;
+    }
+
+    protected override DataTemplate SelectTemplateCore(object item)
+    {
+        var result = item switch
+        {
+            SceneNode => SceneNodeTemplate,
+            EntityNode => EntityNodeTemplate,
+            _ => base.SelectTemplateCore(item)
+        };
+
+        return result!;
+    }
+
+    protected override DataTemplate SelectTemplateCore(object item, DependencyObject container)
+    {
+        return SelectTemplateCore(item);
+    }
+}