[FR] check-repo-hygiene: flag rule files missing from README

Use case

scripts/check-repo-hygiene.mjs catches README bullets pointing at missing rule files, but not the reverse: rule files under rules/ that no README section links. Today rules/ has 257 .mdc files while README.md links 214 unique paths (43 orphans).

Proposal

Add a check (under --only readme or rules) that fails when a rules/*.mdc file is not referenced by any rules/...\.mdc link in README.md. Allow an opt-out list for intentionally unlisted internal rules.

Existing art

Mirror of the existing checkReadmeOnlyExternalListings check in scripts/check-repo-hygiene.mjs.

Not-a-bug caveat

Enhancement, not a defect.

Thanks for maintaining PatrickJS/awesome-cursorrules!