refactor(diff): single DiffViewer replaces DiffModal + WorktreeModal + PlanningDiff

src/ClaudeDo.Ui/Views/Modals/DiffViewerView.axaml.cs

@@ -0,0 +1,41 @@
+using Avalonia.Controls;
+using Avalonia.Input;
+using ClaudeDo.Ui.ViewModels.Modals;
+
+namespace ClaudeDo.Ui.Views.Modals;
+
+public partial class DiffViewerView : Window
+{
+    public DiffViewerView()
+    {
+        InitializeComponent();
+    }
+
+    protected override void OnDataContextChanged(EventArgs e)
+    {
+        base.OnDataContextChanged(e);
+        if (DataContext is DiffViewerViewModel vm)
+            vm.CloseAction = Close;
+
+        // SelectedItem TwoWay binding can miss on Avalonia 12 TreeView — back it
+        // up with SelectionChanged.
+        var tree = this.FindControl<TreeView>("FileTree");
+        if (tree is not null)
+            tree.SelectionChanged += OnFileTreeSelectionChanged;
+    }
+
+    private void OnFileTreeSelectionChanged(object? sender, SelectionChangedEventArgs e)
+    {
+        if (DataContext is DiffViewerViewModel vm && sender is TreeView tree)
+            vm.SelectedNode = tree.SelectedItem as DiffTreeNodeViewModel;
+    }
+
+    private void OnNodeTapped(object? sender, TappedEventArgs e)
+    {
+        if (sender is not Control c) return;
+        if (c.DataContext is not DiffTreeNodeViewModel node) return;
+        if (!node.IsDirectory) return;
+        node.IsExpanded = !node.IsExpanded;
+        e.Handled = true;
+    }
+}