docs: add XML documentation and ConfigManager implementation plans

Add comprehensive XML documentation (param/returns tags) across 132 source
files to improve IntelliSense and API discoverability. Include ConfigManager
design documents and implementation plans for phases 1-9.

NEW/src/Utils/JdeScoping.SecureStoreManager/Views/OpenStoreDialog.axaml.cs

@@ -10,8 +10,14 @@ namespace JdeScoping.SecureStoreManager.Views;
 
 public partial class OpenStoreDialog : Window
 {
+    /// <summary>
+    /// Gets the view model for this dialog.
+    /// </summary>
     public OpenStoreDialogViewModel ViewModel => (OpenStoreDialogViewModel)DataContext!;
 
+    /// <summary>
+    /// Initializes a new instance of the <see cref="OpenStoreDialog"/> class.
+    /// </summary>
     public OpenStoreDialog()
     {
         InitializeComponent();