Update README.md with project details, features, requirements, architecture, and data management for PLib video library manager.

src/PLib.Desktop/App.axaml.cs

@@ -0,0 +1,55 @@
+using Avalonia;
+using Avalonia.Controls.ApplicationLifetimes;
+using Avalonia.Markup.Xaml;
+using Avalonia.Threading;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Hosting;
+using PLib.Desktop.Controls;
+using PLib.Desktop.Imaging;
+using PLib.Desktop.ViewModels;
+using PLib.Desktop.Views;
+
+namespace PLib.Desktop;
+
+// Fully qualified: the PLib.Application namespace shadows the Application type in this assembly.
+public sealed class App : Avalonia.Application
+{
+    private IHost? _host;
+
+    public override void Initialize() => AvaloniaXamlLoader.Load(this);
+
+    public override void OnFrameworkInitializationCompleted()
+    {
+        if (ApplicationLifetime is IClassicDesktopStyleApplicationLifetime desktop)
+        {
+            _host = AppHost.Create(desktop.Args ?? []);
+            _host.Start();
+
+            AsyncImage.Loader = _host.Services.GetRequiredService<ThumbnailCache>();
+
+            var viewModel = _host.Services.GetRequiredService<MainWindowViewModel>();
+            desktop.MainWindow = new MainWindow { DataContext = viewModel };
+            desktop.Exit += OnExit;
+
+            // Kick the first load off once the dispatcher is running, so a failure surfaces
+            // through the view model instead of disappearing into an unobserved task.
+            Dispatcher.UIThread.Post(
+                () => viewModel.InitializeCommand.Execute(null),
+                DispatcherPriority.Background);
+        }
+
+        base.OnFrameworkInitializationCompleted();
+    }
+
+    private void OnExit(object? sender, ControlledApplicationLifetimeExitEventArgs e)
+    {
+        if (_host is null)
+        {
+            return;
+        }
+
+        _host.StopAsync(TimeSpan.FromSeconds(3)).GetAwaiter().GetResult();
+        _host.Dispose();
+        _host = null;
+    }
+}