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

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

src/Explorer.Hosting/DeferredServiceProvider.cs

@@ -0,0 +1,17 @@
+namespace Explorer.Hosting;
+
+public sealed class DeferredServiceProvider : IServiceProvider
+{
+    private IServiceProvider? _inner;
+    private readonly TaskCompletionSource<IServiceProvider> _ready = new(TaskCreationOptions.RunContinuationsAsynchronously);
+
+    public Task<IServiceProvider> Ready => _ready.Task;
+
+    public void Complete(IServiceProvider inner)
+    {
+        _inner = inner;
+        _ready.TrySetResult(inner);
+    }
+
+    public object? GetService(Type serviceType) => _inner?.GetService(serviceType);
+}