fix(infra): scope release-pipeline assertions to checkouts that contain it

The managed-provisioning harness hard-asserted on scripts/release/ files
(packages policy, build.mjs, release shellcheck targets) that ship in a
separate stack slice, so the harness could never pass on this branch and
everything after the first missing-file grep never ran. Gate those
assertions on the pipeline's presence with a loud skip notice; the full
harness now runs end to end here and still asserts the release invariants
on checkouts that include the pipeline.

Co-authored-by: Cursor <cursoragent@cursor.com>