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.Core/ModeCategory.cs

@@ -0,0 +1,9 @@
+namespace Nonemm.Core;
+
+/// The three groups contest rules score and check dupes by.
+public enum ModeCategory
+{
+    Cw,
+    Phone,
+    Digital,
+}