Improve the bandmap window

Remove the status bar and the band name, add the 75 and 150 kHz spans,
add buttons for the callsign size (saved in the settings), draw the scale
in the form's text colour so it shows in the dark theme, mark the carrier
on the VFO bar and place a sideband bar on its side of the carrier, and
show who spotted a station, when, and the comment when the pointer is on it.

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

src/Nonemm.App/Configuration/Settings.cs

@@ -60,6 +60,9 @@ public sealed record Settings
     /// the receiver nears an edge.
     public bool BandmapCentred { get; init; }
 
+    /// The height of the callsigns on the bandmap, in points.
+    public int BandmapTextSize { get; init; } = 12;
+
     /// Moves each incoming CW spot by a few tens of hertz, so the operator has
     /// to find the station by ear. N1MM calls it randomising.
     public bool RandomizeSpots { get; init; }