fix(freeze-panes): flyout matches toolbar width exactly

The flyout's width now tracks the toolbar's own border width (captured
whenever the annotation tools aren't shown, since that's the toolbar's
common/base width) instead of a fixed guess, applied to the FreezePanesView
content each time it opens.

The default FlyoutPresenter adds its own theme padding around content, so
matching the content Width alone still rendered a slightly wider popup than
the toolbar — zeroed via a FlyoutPresenter.noPad style class (FreezePanesView
already supplies its own Margin, so nothing is lost) so the flyout's width
now maps 1:1 to the toolbar's.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Author: sjvrensburg

src/RailReader2/Views/FreezePanesView.axaml

@@ -5,10 +5,10 @@
              x:Class="RailReader2.Views.FreezePanesView"
              x:DataType="vm:MainWindowViewModel">
     <ScrollViewer VerticalScrollBarVisibility="Auto" HorizontalScrollBarVisibility="Disabled">
-        <StackPanel Margin="8,6" Spacing="6" MinWidth="200">
+        <StackPanel Name="RootPanel" Margin="8,6" Spacing="6" HorizontalAlignment="Stretch">
             <TextBlock Text="Freeze panes" FontWeight="SemiBold" />
             <TextBlock Name="CaptionText"
-                       Text="Pin rows / columns in place while the rest of the page scrolls — works on any page."
+                       Text="Pin rows / columns in place while the rest of the page scrolls."
                        TextWrapping="Wrap" Opacity="0.7" />
             <StackPanel Spacing="4">
                 <ToggleButton Name="FreezeRowsButton"

src/RailReader2/Views/ToolBarView.axaml

@@ -11,6 +11,13 @@
             <Setter Property="Margin" Value="3,2" />
             <Setter Property="Background" Value="{DynamicResource SystemControlForegroundBaseMediumLowBrush}" />
         </Style>
+        <!-- The default FlyoutPresenter adds its own theme padding around content, so a content Width
+             set to match the toolbar's width still renders a wider popup than the toolbar. Zeroed here
+             (FreezePanesView supplies its own Margin) so the freeze flyout's Width maps 1:1 to what's
+             actually on screen. -->
+        <Style Selector="FlyoutPresenter.noPad">
+            <Setter Property="Padding" Value="0" />
+        </Style>
     </UserControl.Styles>
 
     <Border Name="RootBorder"

src/RailReader2/Views/ToolBarView.axaml.cs

@@ -67,13 +67,24 @@ public ToolBarView()
         // with the toolbar's bottom-left edge, regardless of where the Freeze button sits in the row.
         // Button.Flyout would anchor to the button itself instead, so this is wired manually.
         _freezeFlyout.Placement = PlacementMode.BottomEdgeAlignedLeft;
+        _freezeFlyout.FlyoutPresenterClasses.Add("noPad");
+        // Track the toolbar's width whenever the annotation tools aren't shown (its "base" width — the
+        // common case, since freeze is unrelated to annotation mode), so the flyout matches it exactly
+        // even if opened while the annotation section happens to be expanded.
+        RootBorder.LayoutUpdated += (_, _) =>
+        {
+            if (!AnnotationSection.IsVisible) _baseToolbarWidth = RootBorder.Bounds.Width;
+        };
         FreezeButton.Click += (_, _) =>
         {
-            if (_freezeFlyout.IsOpen) _freezeFlyout.Hide();
-            else _freezeFlyout.ShowAt(RootBorder);
+            if (_freezeFlyout.IsOpen) { _freezeFlyout.Hide(); return; }
+            _freezeView.Width = _baseToolbarWidth > 0 ? _baseToolbarWidth : RootBorder.Bounds.Width;
+            _freezeFlyout.ShowAt(RootBorder);
         };
     }
 
+    private double _baseToolbarWidth;
+
     private void OnVmPropertyChanged(object? sender, PropertyChangedEventArgs args)
     {
         switch (args.PropertyName)