manager: migrate base project structure & deps

ModpackUpdater.Apps.Manager/Ui/MainWindow.axaml.cs

@@ -0,0 +1,13 @@
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Markup.Xaml;
+
+namespace ModpackUpdater.Apps.Manager.Ui;
+
+public partial class MainWindow : Window
+{
+    public MainWindow()
+    {
+        InitializeComponent();
+    }
+}