feat(09-03): add chart panel to StorageView with toggle and localization

- Update StorageView.xaml: DataGrid top, GridSplitter, chart panel bottom
- Add PieChart and CartesianChart with MultiDataTrigger visibility
- Add radio buttons for donut/bar chart toggle in left panel
- Create BytesLabelConverter for chart tooltip formatting
- Add stor.chart.* localization keys in EN and FR resx files

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

SharepointToolbox/Views/Converters/BytesLabelConverter.cs

@@ -0,0 +1,23 @@
+using System.Globalization;
+using System.Windows.Data;
+
+namespace SharepointToolbox.Views.Converters;
+
+/// <summary>
+/// Converts a long byte value to a human-readable label for chart axes and tooltips.
+/// Similar to BytesConverter but implements IValueConverter for XAML binding.
+/// </summary>
+public class BytesLabelConverter : IValueConverter
+{
+    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
+    {
+        if (value is not long bytes) return value?.ToString() ?? "";
+        if (bytes < 1024) return $"{bytes} B";
+        if (bytes < 1024 * 1024) return $"{bytes / 1024.0:F1} KB";
+        if (bytes < 1024 * 1024 * 1024) return $"{bytes / (1024.0 * 1024):F1} MB";
+        return $"{bytes / (1024.0 * 1024 * 1024):F2} GB";
+    }
+
+    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
+        => throw new NotSupportedException();
+}