pkgx-style shebangs (#!/usr/bin/env -S pkgx python@3.11) are not rewritten at install

Registry artifacts mirrored from pkgx carry scripts that resolve their interpreter through pkgx at run time. pantry install aws.amazon.com/cli installs bin/aws with #!/usr/bin/env -S pkgx python@3.11, so running it fails with "pkgx: No such file or directory" (and with pkgx present, pkgx would fetch its own python). Pantry should point these shebangs at the interpreter it installed (installing a satisfying one if the tree has none), for every package.