Add the Avalonia application and the station network

The entry window types contacts and colours them as they are typed; the log,
check, bandmap, score and packet windows read the same session. Contacts are
shared with the other stations of a multi-operator entry in N1MM's contact
message, so an N1MM station on the same network sees them too.

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

src/Nonemm.App/Configuration/Settings.cs

@@ -0,0 +1,117 @@
+using System.Text.Json;
+using System.Text.Json.Serialization;
+using Nonemm.Core;
+
+namespace Nonemm.App.Configuration;
+
+/// What the program remembers between runs.
+public sealed record Settings
+{
+    public string DatabasePath { get; init; } = "";
+
+    public int ContestNumber { get; init; }
+
+    public StoredStation Station { get; init; } = new();
+
+    public string ClusterHost { get; init; } = "";
+
+    public int ClusterPort { get; init; } = 7373;
+
+    public IReadOnlyList<string> ClusterCommands { get; init; } = [];
+
+    public string RigctldHost { get; init; } = "127.0.0.1";
+
+    public int RigctldPort { get; init; } = 4532;
+
+    public bool RadioEnabled { get; init; }
+
+    public bool ClusterEnabled { get; init; }
+
+    public string NetworkStationName { get; init; } = "";
+
+    public int NetworkPort { get; init; } = 12060;
+
+    public bool NetworkEnabled { get; init; }
+
+    public IReadOnlyList<string> NetworkPeers { get; init; } = [];
+
+    public static Settings Load(string path)
+    {
+        if (!File.Exists(path))
+        {
+            return new Settings();
+        }
+        try
+        {
+            return JsonSerializer.Deserialize(File.ReadAllText(path), SettingsJson.Default.Settings)
+                ?? new Settings();
+        }
+        catch (JsonException)
+        {
+            // a settings file that will not parse is replaced rather than
+            // stopping the program before a contest
+            return new Settings();
+        }
+    }
+
+    public void Save(string path) =>
+        File.WriteAllText(path, JsonSerializer.Serialize(this, SettingsJson.Default.Settings));
+}
+
+/// The operator's station as it is stored, kept separate from `StationInfo` so
+/// the file format does not follow every change to the domain type.
+public sealed record StoredStation
+{
+    public string Callsign { get; init; } = "";
+
+    public int CqZone { get; init; }
+
+    public int ItuZone { get; init; }
+
+    public string Continent { get; init; } = "";
+
+    public string CountryPrefix { get; init; } = "";
+
+    public string State { get; init; } = "";
+
+    public string Province { get; init; } = "";
+
+    public string ArrlSection { get; init; } = "";
+
+    public string GridSquare { get; init; } = "";
+
+    public string County { get; init; } = "";
+
+    public string Name { get; init; } = "";
+
+    public string Power { get; init; } = "";
+
+    public string Club { get; init; } = "";
+
+    public int Check { get; init; }
+
+    public string Precedence { get; init; } = "A";
+
+    public StationInfo ToStationInfo() => new()
+    {
+        Callsign = Callsign,
+        CqZone = CqZone,
+        ItuZone = ItuZone,
+        Continent = Continent,
+        CountryPrefix = CountryPrefix,
+        State = State,
+        Province = Province,
+        ArrlSection = ArrlSection,
+        GridSquare = GridSquare,
+        County = County,
+        Name = Name,
+        Power = Power,
+        Club = Club,
+        Check = Check,
+        Precedence = Precedence,
+    };
+}
+
+[JsonSerializable(typeof(Settings))]
+[JsonSourceGenerationOptions(WriteIndented = true)]
+internal sealed partial class SettingsJson : JsonSerializerContext;