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

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

tests/Explorer.Application.Tests/FfmpegLocatorTests.cs

@@ -0,0 +1,30 @@
+using Explorer.Application;
+
+namespace Explorer.Application.Tests;
+
+public class FfmpegLocatorTests
+{
+    [Fact]
+    public void Prefers_the_configured_path_when_it_exists()
+    {
+        var path = @"C:\Tools\ffmpeg.exe";
+        Assert.Equal(path, FfmpegLocator.Find(path, fileExists: p => p == path, pathVariable: ""));
+    }
+
+    [Fact]
+    public void Finds_ffmpeg_on_PATH_when_not_configured()
+    {
+        var found = FfmpegLocator.Find(
+            null,
+            fileExists: p => p.Equals(@"D:\bin\ffmpeg.exe", StringComparison.OrdinalIgnoreCase),
+            pathVariable: @"C:\Windows;D:\bin");
+        Assert.Equal(@"D:\bin\ffmpeg.exe", found);
+    }
+
+    [Fact]
+    public void Returns_null_when_ffmpeg_is_missing()
+    {
+        Assert.Null(FfmpegLocator.Find(null, fileExists: _ => false, pathVariable: @"C:\none"));
+        Assert.Contains("FFmpeg", FfmpegLocator.MissingHint, StringComparison.OrdinalIgnoreCase);
+    }
+}