Name a monospace font list instead of the generic monospace

The generic name only resolves through fontconfig, so on Windows the
windows fell back to the proportional default.

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

src/Nonemm.App/Windows/ScoreWindow.axaml.cs

@@ -1,3 +1,4 @@
+using Nonemm.App.Theming;
 using Avalonia.Controls;
 using Nonemm.Contests;
 using Nonemm.Core;
@@ -109,7 +110,7 @@ public sealed partial class ScoreWindow : RefreshableWindow
             TextBlock text = new()
             {
                 Text = cells[column],
-                FontFamily = new Avalonia.Media.FontFamily("monospace"),
+                FontFamily = Fonts.Mono,
                 FontSize = 13,
                 Opacity = header ? 1.0 : 0.85,
                 Margin = new Avalonia.Thickness(0, 2, 8, 2),