Add WPF/WebView2 desktop host project

- Program.cs with application bootstrap and DI setup
- index.html entry point with Blazor WebView
- Application stylesheet

src/Duempelkas.Desktop/Program.cs

@@ -0,0 +1,74 @@
+using Duempelkas.Infrastructure;
+using Duempelkas.Infrastructure.Persistence;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.DependencyInjection;
+using Photino.Blazor;
+
+namespace Duempelkas.Desktop;
+
+class Program
+{
+    [STAThread]
+    static void Main(string[] args)
+    {
+        var appBuilder = PhotinoBlazorAppBuilder.CreateDefault(args);
+
+        var dbPath = Path.Combine(AppContext.BaseDirectory, "duempelkas.db");
+        appBuilder.Services.AddInfrastructure($"Data Source={dbPath}");
+
+        appBuilder.RootComponents.Add<Duempelkas.App.Components.App>("app");
+
+        var app = appBuilder.Build();
+
+        app.MainWindow.StartUrl = PhotinoWebViewManager.AppBaseUri;
+
+        using (var scope = app.Services.CreateScope())
+        {
+            var db = scope.ServiceProvider.GetRequiredService<FinanceDbContext>();
+            db.Database.Migrate();
+        }
+
+        // Load saved window size or use defaults
+        var settingsPath = Path.Combine(
+            Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData),
+            "Duempelkas", "window.json");
+
+        int savedWidth = 1280, savedHeight = 768;
+        if (File.Exists(settingsPath))
+        {
+            try
+            {
+                var json = File.ReadAllText(settingsPath);
+                var doc = System.Text.Json.JsonDocument.Parse(json);
+                savedWidth = doc.RootElement.GetProperty("width").GetInt32();
+                savedHeight = doc.RootElement.GetProperty("height").GetInt32();
+            }
+            catch { /* use defaults on parse error */ }
+        }
+
+        app.MainWindow
+            .SetTitle("Dümpelkas – Kassenbuch")
+            .SetSize(savedWidth, savedHeight)
+            .SetUseOsDefaultSize(false);
+
+        // Persist window size on resize
+        app.MainWindow.RegisterSizeChangedHandler((_, size) =>
+        {
+            try
+            {
+                var dir = Path.GetDirectoryName(settingsPath)!;
+                Directory.CreateDirectory(dir);
+                File.WriteAllText(settingsPath,
+                    System.Text.Json.JsonSerializer.Serialize(new { width = size.Width, height = size.Height }));
+            }
+            catch { /* ignore save errors */ }
+        });
+
+        AppDomain.CurrentDomain.UnhandledException += (sender, error) =>
+        {
+            app.MainWindow.ShowMessage("Schwerwiegender Fehler", error.ExceptionObject.ToString());
+        };
+
+        app.Run();
+    }
+}