feat(08-03): add simplified mode UI to PermissionsView

- Add Display Options GroupBox with Simplified Mode toggle and Simple/Detailed radio buttons
- Add summary panel with color-coded risk level cards bound to Summaries collection
- DataGrid binds to ActiveItemsSource, rows color-coded by RiskLevel via DataTriggers
- SimplifiedLabels column visible only in simplified mode via BooleanToVisibilityConverter
- DataGrid collapses in Simple mode via MultiDataTrigger on IsSimplifiedMode+IsDetailView
- Create InvertBoolConverter for radio button inverse binding

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

SharepointToolbox/Core/Converters/InvertBoolConverter.cs

@@ -0,0 +1,18 @@
+using System.Globalization;
+using System.Windows.Data;
+
+namespace SharepointToolbox.Core.Converters;
+
+/// <summary>
+/// Inverts a boolean value. Used for radio button binding where
+/// one option is the inverse of the bound property.
+/// </summary>
+[ValueConversion(typeof(bool), typeof(bool))]
+public class InvertBoolConverter : IValueConverter
+{
+    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
+        => value is bool b ? !b : value;
+
+    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
+        => value is bool b ? !b : value;
+}