Add shared export infrastructure

LehrerApp.Desktop/Views/Groups/ExamEvaluationDialog.axaml.cs

@@ -1,7 +1,8 @@
 using Avalonia.Controls;
 using Avalonia.Interactivity;
-using Avalonia.Platform.Storage;
+using LehrerApp.Desktop.Services;
 using LehrerApp.Desktop.ViewModels.Groups;
+using Microsoft.Extensions.DependencyInjection;
 
 namespace LehrerApp.Desktop.Views.Groups;
 
@@ -15,15 +16,9 @@ public partial class ExamEvaluationDialog : Window
         var topLevel = TopLevel.GetTopLevel(this);
         if (topLevel is null) return;
 
-        var file = await topLevel.StorageProvider.SaveFilePickerAsync(new FilePickerSaveOptions
-        {
-            Title             = "Klausurauswertung exportieren",
-            SuggestedFileName = $"Auswertung_{vm.ExamTitle}.csv",
-            FileTypeChoices   = [new FilePickerFileType("CSV-Dateien") { Patterns = ["*.csv"] }],
-        });
-
-        if (file is null) return;
-        await File.WriteAllTextAsync(file.Path.LocalPath, vm.ExportCsv());
+        var export = ExportFile.Csv("Klausurauswertung exportieren",
+            $"Auswertung_{vm.ExamTitle}.csv", vm.ExportCsv());
+        await App.Services.GetRequiredService<ExportService>().SaveAsync(topLevel.StorageProvider, export);
     }
 
     private void OnClose(object? sender, RoutedEventArgs e) => Close();