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/BandmapView.cs

@@ -1,3 +1,4 @@
+using Nonemm.App.Theming;
 using System.Globalization;
 using Avalonia;
 using Avalonia.Controls;
@@ -37,7 +38,7 @@ public sealed class BandmapView : Control
     /// Past the band edge. The slice can reach there when the radio does.
     private static readonly IBrush OutsideBrush = new SolidColorBrush(Color.FromRgb(0xC0, 0x39, 0x2B), 0.13);
 
-    private readonly Typeface typeface = new(new FontFamily("monospace"));
+    private readonly Typeface typeface = new(Fonts.Mono);
     private IReadOnlyList<BandmapLabel> placed = [];
     private BandmapScale scale = new(Bands.Band20M.Low, Bands.Band20M.High, 1);