Add CW keying, function key messages and the documentation

The function keys send through cwdaemon or a WinKeyer, with N1MM's message
macros. Escape stops sending.

Settings are read with the reflection serializer rather than a generated one:
the generated one hands back null for every property the file leaves out
instead of the value the property is declared with, which crashed the program
the first time a new setting was added.

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

src/Nonemm.App/Windows/EntryWindow.Menu.cs

@@ -254,6 +254,27 @@ public sealed partial class EntryWindow
         }
     }
 
+    private async void OnKeyerSettings(object? sender, RoutedEventArgs e)
+    {
+        KeyerDialog dialog = new(session.Settings);
+        Settings? updated = await dialog.ShowDialog<Settings?>(this);
+        if (updated is null)
+        {
+            return;
+        }
+        session.Save(updated);
+        try
+        {
+            session.ApplyKeyerSettings();
+            Status(updated.KeyerKind == "none" ? "no keyer" : $"keyer: {updated.KeyerKind}");
+        }
+        catch (Exception error) when (error is InvalidOperationException or IOException or UnauthorizedAccessException)
+        {
+            Status($"could not open the keyer: {error.Message}");
+        }
+        BuildFunctionKeys();
+    }
+
     private async void OnDownloadCountryFile(object? sender, RoutedEventArgs e) =>
         await Download(
             downloader => downloader.DownloadCountryFileAsync(session.Paths.CountryFile),