ShowErrorWindow now actually shows the ErrorWindow

PcgsInvUi/Views/ErrorWindow.axaml.cs

@@ -0,0 +1,11 @@
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Markup.Xaml;
+
+namespace PcgsInvUi.Views; 
+
+public partial class ErrorWindow : Window {
+    public ErrorWindow() {
+        InitializeComponent();
+    }
+}