Add the core, contest, storage and format layers

Frequencies, bands, modes, callsigns, grid squares and the country file live in
Nonemm.Core. Nonemm.Contests holds the scoring engine and CQ WW and CQ WPX.
Nonemm.Storage writes N1MM's DXLOG schema, and Nonemm.Formats writes Cabrillo
3.0 and reads and writes ADIF.

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

src/Nonemm.Contests/Contest.cs

@@ -0,0 +1,41 @@
+using Nonemm.Core;
+
+namespace Nonemm.Contests;
+
+/// One contest's rules: what is exchanged, when a station may be worked again,
+/// what a contact scores and which multipliers it brings in.
+public interface Contest
+{
+    /// The short name the log stores, e.g. `CQWW`.
+    string Name { get; }
+
+    string DisplayName { get; }
+
+    /// The name the sponsor's Cabrillo header asks for.
+    string CabrilloName { get; }
+
+    IReadOnlyList<ExchangeField> ExchangeFields { get; }
+
+    /// Up to three names, in the order the score summary shows them.
+    IReadOnlyList<string> MultiplierNames { get; }
+
+    DupeScope DupeScope { get; }
+
+    /// True when serial numbers count up across the whole contest rather than
+    /// per band.
+    bool HasSerialNumbers { get; }
+
+    /// The modes the contest runs; empty means any.
+    IReadOnlyList<ModeCategory> Modes { get; }
+
+    string SentExchangeFor(StationInfo me);
+
+    int PointsFor(QsoContext qso);
+
+    IReadOnlyList<Multiplier> MultipliersFor(QsoContext qso);
+
+    int TotalScore(ScoreTally tally);
+
+    /// The exchange columns of this contact's Cabrillo line.
+    CabrilloExchange CabrilloExchange(Qso qso, StationInfo me);
+}