refactor(securestore): remove password-based authentication in favor of key-file only

Simplify SecureStore by removing MasterKeyEnvVar and password-based methods, leaving only key-file authentication for better security practices.

NEW/tests/JdeScoping.SecureStoreManager.Tests/Views/NewStoreDialogTests.cs

@@ -45,15 +45,15 @@ public class NewStoreDialogTests
     }
 
     [AvaloniaFact]
-    public void NewStoreDialog_HasRadioButtons()
+    public void NewStoreDialog_HasKeyFilePathTextBox()
     {
         // Arrange & Act
         var dialog = new NewStoreDialog();
         dialog.Show();
 
-        // Assert
-        var radioButtons = dialog.GetVisualDescendants().OfType<RadioButton>().ToList();
-        radioButtons.Count.ShouldBeGreaterThanOrEqualTo(2);
+        // Assert - Should have at least 2 text boxes: store path and key file path
+        var textBoxes = dialog.GetVisualDescendants().OfType<TextBox>().ToList();
+        textBoxes.Count.ShouldBeGreaterThanOrEqualTo(2);
     }
 
     [AvaloniaFact]