DOCFIX-137: repo-lint L8 -- enforceable guide<->skill coupling guard ...

Make 'sweep the skill when the guide changes' a hard gate, not a note (skill-lag hit
twice: DOCFIX-135/136). L8 pins the Jenkins+K8s guide's sha256 in
clientdocs/guide-skill-coupling.txt; any guide change FAILS repo-lint (naming the
skill files to review) until re-recorded with --record-guide-skill-coupling. Mirrors
the L7 sweep-receipt pattern. Harness +5 (28/28), gauntlet 39/39, lint 0 fail.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>