Runs after BuildManifest and decorates the persisted %Ash.Info.Manifest{} with ash_typescript-specific metadata.

After this transformer, every persisted lookup — :manifest, :resource_lookup, :action_lookup, :type_lookup — refers to the decorated spec. Downstream readers (verifiers, runtime, codegen) should pull the manifest and lookups from here.

See AshTypescript.Manifest.Decorator for what gets decorated.