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

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

src/Explorer.FileOperations/TransferQueue.cs

@@ -157,6 +157,17 @@ public sealed class TransferQueue : BackgroundService, ITransferHost
             CreatedUtc = DateTimeOffset.UtcNow
         }, cancellationToken);
 
+    public Task EnqueueConvertAsync(string sourcePath, string destinationPath, ConversionKind kind, CancellationToken cancellationToken = default)
+        => EnqueueAsync(new TransferJob
+        {
+            Op = TransferOp.Convert,
+            SourcePath = sourcePath,
+            DestinationPath = destinationPath,
+            Status = TransferStatus.Queued,
+            CreatedUtc = DateTimeOffset.UtcNow,
+            AdditionalSources = [kind.ToString()]
+        }, cancellationToken);
+
     public void PauseAll()
     {
         _queuePaused = true;