Add public bundle manifest package

pkg/bundle/doc.go

@@ -0,0 +1,8 @@
+// Package bundle provides producer-facing helpers for distributor source
+// bundle manifests.
+//
+// A source bundle is a local directory containing a manifest.json file and the
+// files listed by that manifest. This package owns the public manifest model,
+// digest calculation, path validation, manifest parsing, manifest building, and
+// local bundle validation used by Go producer applications.
+package bundle