feat(bake): publish validated pak artifacts atomically

src/AcDream.Content/Pak/PakWriter.cs

@@ -30,6 +30,7 @@ public sealed class PakWriter : IDisposable {
         // (the default-0 footgun; PakReader rejects any version but
         // PakFormat.CurrentFormatVersion).
         _headerTemplate.FormatVersion = PakFormat.CurrentFormatVersion;
+        _headerTemplate.BakeToolVersion = PakFormat.CurrentBakeToolVersion;
 
         // Write a header placeholder now; finalized in Finish() once TocOffset/TocCount are known.
         _headerTemplate.WriteTo(_stream);