Add queued FFmpeg conversion and finish splitting the window from the host.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/Explorer.App/ConvertWindow.xaml.cs

@@ -0,0 +1,41 @@
+using System.Windows;
+using Explorer.Presentation.ViewModels;
+
+namespace Explorer.App;
+
+public partial class ConvertWindow : Window
+{
+    public ConvertWindow(ConvertViewModel vm)
+    {
+        InitializeComponent();
+        DataContext = vm;
+        vm.CloseRequested += (_, _) =>
+        {
+            try
+            {
+                DialogResult = true;
+            }
+            catch (InvalidOperationException)
+            {
+                // not shown as a dialog
+            }
+
+            Close();
+        };
+    }
+
+    private void OnBrowseDest(object sender, RoutedEventArgs e)
+    {
+        var picker = new Microsoft.Win32.OpenFolderDialog
+        {
+            Title = "Convert to",
+            Multiselect = false
+        };
+        if (picker.ShowDialog(this) == true
+            && !string.IsNullOrWhiteSpace(picker.FolderName)
+            && DataContext is ConvertViewModel vm)
+        {
+            vm.DestPath = picker.FolderName;
+        }
+    }
+}