Leave the cluster's time out of the bandmap hover comment

A cluster line ends with the time of the spot, which the age on the
first line already says.

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

src/Nonemm.Spotting/SpotDescription.cs

@@ -1,11 +1,12 @@
 using System.Globalization;
+using System.Text.RegularExpressions;
 
 namespace Nonemm.Spotting;
 
 /// What the bandmap shows when the pointer rests on a spot: the frequency,
 /// who spotted it and how long ago, and the comment if it says more than the
 /// sideband.
-public static class SpotDescription
+public static partial class SpotDescription
 {
     public static string Of(Spot spot, DateTime? nowUtc = null)
     {
@@ -19,6 +20,9 @@ public static class SpotDescription
         return comment.Length > 0 ? $"{first}\n{comment}" : first;
     }
 
+    [GeneratedRegex(@"\s*\b\d{4}Z$", RegexOptions.IgnoreCase)]
+    private static partial Regex TrailingTime();
+
     private static string Age(TimeSpan span)
     {
         int minutes = Math.Max(0, (int)span.TotalMinutes);
@@ -34,7 +38,9 @@ public static class SpotDescription
     private static string Comment(string text)
     {
         string clean = new([.. text.Where(c => !char.IsControl(c))]);
-        clean = clean.Trim();
+        // the cluster ends its line with the time of the spot, which the age
+        // already says
+        clean = TrailingTime().Replace(clean, "").Trim();
         return clean.ToUpperInvariant() is "LSB" or "USB" or "SSB" ? "" : clean;
     }
 }