Fix example data dialog to respect 'No' response

Previously, clicking "No" in the confirmation dialog would still proceed to
load example data. Now both Cancel and No properly abort the operation.

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

CutList/Presenters/MainFormPresenter.cs

@@ -180,7 +180,7 @@ namespace CutList.Presenters
             {
                 var result = _view.AskYesNoCancel("Are you sure you want to clear the current data?", "Clear Data");
 
-                if (result == null) // Cancel
+                if (result == null || !result.Value)
                     return;
 
                 LoadExampleData(result.Value);