Capture mesh-catalog at feat/r4g (2246ccc4) with the templates its manifests name and its predefined.json, and lay the copy out as a repository's root

The catalogue's manifests moved their content into template files and fall back to predefined keys, so a copy of
module.json alone no longer passes the catalogue's own check; the bus's Dockerfile is gone from the catalogue.

internal/beside/beside.go

@@ -73,6 +73,11 @@ func Dir(t testing.TB, repository string) string {
 		}
 		return os.WriteFile(into, raw, 0o644)
 	})
+	if err == nil {
+		// The copy stands at its repository's root, as the clone does: what is read from a repository's root
+		// (the catalogue's predefined.json, found above a manifest by its .git) is found in the copy too.
+		err = os.WriteFile(filepath.Join(dir, ".git"), nil, 0o644)
+	}
 	if err != nil {
 		t.Fatalf("the captured copy of %s could not be laid out: %v", repository, err)
 	}