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/App.axaml.cs

@@ -0,0 +1,25 @@
+using Avalonia;
+using Avalonia.Controls.ApplicationLifetimes;
+using Avalonia.Markup.Xaml;
+using Nonemm.App.Configuration;
+using Nonemm.App.Windows;
+
+namespace Nonemm.App;
+
+public partial class App : Application
+{
+    public override void Initialize() => AvaloniaXamlLoader.Load(this);
+
+    public override void OnFrameworkInitializationCompleted()
+    {
+        if (ApplicationLifetime is IClassicDesktopStyleApplicationLifetime desktop)
+        {
+            UserPaths paths = UserPaths.Default();
+            paths.CreateFolders();
+            AppSession session = new(paths, Settings.Load(paths.SettingsFile));
+            desktop.MainWindow = new EntryWindow(session);
+            desktop.ShutdownRequested += (_, _) => session.Dispose();
+        }
+        base.OnFrameworkInitializationCompleted();
+    }
+}