Mark a dupe in the contact type column, as N1MM does

N1MM writes a contact type on every contact it logs: `D` for a station
already worked, `N` for one the entry may not work at all, and empty for an
ordinary contact. Nothing here wrote the column, so a dupe counted as a
contact worth no points instead of dropping out of the score, and the two
places that read the column did nothing: the QTC pile offered dupes that
N1MM leaves out, and the statistics window could not leave dupes out either.

The marking is in one place, `ContestLog.ApplyVerdict`, and every contest is
marked the same way. What changes between contests is what counts as a dupe
and which stations are workable, and both come from the contest, as they do
in N1MM's `Contact.IsDupe`. No contest module in N1MM marks differently. Our
own callsign is not workable either, which is what N1MM adds on top of the
contest rule.

Two details follow N1MM as well: QTC traffic keeps an empty column, because
its `IsDupe` only marks a row while the program is logging contacts; and a
mark that came with the contact stands, because N1MM marks a contact when it
logs or edits one and never clears marks in a pass over the log. Editing a
contact clears the column so it is worked out again, which is what N1MM does
at the same point: an edit can move a contact to a band where it is no
longer a dupe.

A dupe is now out of the score altogether — contacts, points and multipliers
— which is N1MM's `ScoreClass.AddContact`. The QSO count still counts WAE
QTC rows as contacts; that is the other half of the scoring audit's item 14.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0157i7PiZyqBkquxS9A6FTdQ

src/Nonemm.Session/QsoEditor.cs

@@ -67,7 +67,16 @@ public sealed class QsoEditor
     public QsoEdit Apply(Qso qso, QsoField field, string text)
     {
         QsoEdit edit = Applied(qso, field, text);
-        return edit.IsAccepted ? edit : edit with { Field = field };
+        if (!edit.IsAccepted)
+        {
+            return edit with { Field = field };
+        }
+        // the contact type is left for the log to work out again: an edit can
+        // move a contact to a band where it is no longer a dupe. N1MM works
+        // it out again at the same point
+        return edit.Result is { } changed
+            ? edit with { Result = changed with { ContactType = "" } }
+            : edit;
     }
 
     /// Applies several fields in one go, stopping at the first value the