feat(ui): add conflict resolution dialog for planning merge-all

Opens a modal when PlanningMergeConflict fires, listing conflicted files
with options to open in VS Code, continue, or abort the merge.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/ClaudeDo.Ui/Views/Planning/ConflictResolutionView.axaml.cs

@@ -0,0 +1,26 @@
+using Avalonia.Controls;
+using Avalonia.Input;
+using ClaudeDo.Ui.ViewModels.Planning;
+
+namespace ClaudeDo.Ui.Views.Planning;
+
+public partial class ConflictResolutionView : Window
+{
+    public ConflictResolutionView()
+    {
+        InitializeComponent();
+    }
+
+    protected override void OnDataContextChanged(EventArgs e)
+    {
+        base.OnDataContextChanged(e);
+        if (DataContext is ConflictResolutionViewModel vm)
+            vm.CloseRequested = Close;
+    }
+
+    private void TitleBar_PointerPressed(object? sender, PointerPressedEventArgs e)
+    {
+        if (e.GetCurrentPoint(this).Properties.IsLeftButtonPressed)
+            BeginMoveDrag(e);
+    }
+}