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.Session/ContestDefinitions.cs

@@ -0,0 +1,51 @@
+using Nonemm.Contests;
+using Nonemm.Core;
+using Nonemm.Storage;
+
+namespace Nonemm.Session;
+
+/// Turns a contest's rules into the definition row N1MM keeps in the `Contest`
+/// table, which it reads when it opens a log.
+public static class ContestDefinitions
+{
+    public static ContestDefinition For(Contest contest)
+    {
+        IReadOnlyList<string> mults = contest.MultiplierNames;
+        return new ContestDefinition
+        {
+            Name = contest.Name,
+            DisplayName = contest.DisplayName,
+            CabrilloName = contest.CabrilloName,
+            Mode = ModeOf(contest),
+            DupeType = DupeTypeOf(contest.DupeScope),
+            Multiplier1Name = NameAt(mults, 0),
+            Multiplier2Name = NameAt(mults, 1),
+            Multiplier3Name = NameAt(mults, 2),
+        };
+    }
+
+    private static string ModeOf(Contest contest)
+    {
+        if (contest.Modes.Count != 1)
+        {
+            return "BOTH";
+        }
+        return contest.Modes[0] switch
+        {
+            ModeCategory.Cw => "CW",
+            ModeCategory.Phone => "SSB",
+            _ => "RTTY",
+        };
+    }
+
+    private static int DupeTypeOf(DupeScope scope) => scope switch
+    {
+        DupeScope.Once => 1,
+        DupeScope.PerBandAndMode => 3,
+        DupeScope.Never => 4,
+        _ => 2,
+    };
+
+    private static string NameAt(IReadOnlyList<string> names, int at) =>
+        at < names.Count ? names[at] : "N/A";
+}