Draw the line under the selected tab in the text colour

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

src/Nonemm.App/App.axaml.cs

@@ -66,6 +66,8 @@ public partial class App : Application
         {
             Set(key, theme.FieldForeground);
         }
+        // the line under the selected tab, which the Fluent blue leaves faint on a dark form
+        Set("TabItemHeaderSelectedPipeFill", theme.FormForeground);
         Set("ButtonBackground", theme.ButtonBackground);
         Set("ButtonBackgroundPointerOver", Lighter(theme.ButtonBackground));
         Set("ButtonBackgroundPressed", Darker(theme.ButtonBackground));