chore: resolve merge conflicts with dev

Merged dev into PR branch, resolving conflicts:
- pkg/io/local/client.go: kept PR's Open(fs.File) and Create methods,
  removed dev's Open(goio.ReadCloser); kept PR's relative path handling
- pkg/io/io.go: removed duplicate Open(goio.ReadCloser) from Medium
  interface and MockMedium, keeping PR's Open(fs.File) + Create
- pkg/release/release.go: kept PR's parameter naming (fs) and
  build.WriteChecksumFile abstraction, removed inlined checksum code

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

pkg/io/local/client.go

@@ -48,6 +48,7 @@ func (m *Medium) path(p string) string {
 		return clean
 	}
 
+
 	// Join cleaned relative path with root
 	return filepath.Join(m.root, clean)
 }