Add Explorer Workbench with hierarchical, off-UI Storage analysis.

Storage queries run in the background with cancellation and covering indexes so switching views no longer freezes the UI.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/Explorer.App/PromptWindow.xaml.cs

@@ -0,0 +1,30 @@
+using System.Windows;
+
+namespace Explorer.App;
+
+public partial class PromptWindow : Window
+{
+    public PromptWindow(string title, string message, string initial)
+    {
+        InitializeComponent();
+        Title = title;
+        Message.Text = message;
+        Input.Text = initial;
+        Input.SelectAll();
+        Loaded += (_, _) => Input.Focus();
+    }
+
+    public string Value => Input.Text;
+
+    private void OnOk(object sender, RoutedEventArgs e)
+    {
+        DialogResult = true;
+        Close();
+    }
+
+    public static string? Ask(Window owner, string title, string message, string initial)
+    {
+        var dlg = new PromptWindow(title, message, initial) { Owner = owner };
+        return dlg.ShowDialog() == true ? dlg.Value : null;
+    }
+}