Lower default strip concurrency to 3

.gitignore

@@ -3,3 +3,4 @@ obj/
 *.user
 history.json
 settings.json
+*.zip

MainWindow.xaml.cs

@@ -16,7 +16,7 @@ namespace Futonizer;
 public partial class MainWindow : FluentWindow
 {
     private const int MaxConcurrentScans = 10;
-    private const int MaxConcurrentStrips = 5;
+    private const int MaxConcurrentStrips = 3;
 
     private AppSettings _settings = new();
     private readonly ObservableCollection<QueuedFileItem> _fileQueue = new();