Write what N1MM needs before it will open a log

Checked by opening a log this program wrote in N1MM 1.0.11031. Three things it
rejected:

- a log naming a contest with no row in the Contest table throws "No current
  row" in Contest.FromRow, so the definition row is written whenever a contest
  is opened;
- an empty overlay category is answered with "Invalid Overlay Category:", so an
  entry with no overlay now says "N/A", and the dialog offers N1MM's list;
- the sent exchange omits the report, which is what N1MM's own contest dialog
  asks for.

With those three fixed N1MM opens the log and shows the contacts.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/Nonemm.Contests/Rules/CqWorldWide.cs

@@ -31,8 +31,9 @@ public sealed class CqWorldWide : Contest
 
     public IReadOnlyList<ModeCategory> Modes => [mode];
 
-    public string SentExchangeFor(StationInfo me) =>
-        $"{DefaultReport()} {me.CqZone}";
+    /// The report is fixed for the whole contest, so the sent exchange is the
+    /// zone alone, which is also what N1MM stores.
+    public string SentExchangeFor(StationInfo me) => me.CqZone.ToString();
 
     public int PointsFor(QsoContext qso)
     {
@@ -83,5 +84,4 @@ public sealed class CqWorldWide : Contest
 
     private string ModeLabel() => mode == ModeCategory.Cw ? "CW" : "SSB";
 
-    private string DefaultReport() => mode == ModeCategory.Cw ? "599" : "59";
 }