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/ViewModels/SecretItemViewModel.cs

@@ -13,6 +13,12 @@ public class SecretItemViewModel : ViewModelBase
     private bool _isValueVisible;
     private const string MaskedValue = "********";
 
+    /// <summary>
+    /// Initializes a new instance of the <see cref="SecretItemViewModel"/> class.
+    /// </summary>
+    /// <param name="key">The secret key name.</param>
+    /// <param name="value">The secret value.</param>
+    /// <param name="clipboardService">The clipboard service for copy operations.</param>
     public SecretItemViewModel(string key, string value, IClipboardService clipboardService)
     {
         Key = key;