SKILL-06 flagged deprecated compatibility shims for missing a "Use when"
trigger phrase. Deprecated skills omit it on purpose so users are steered
to their replacement, so exempt them from that specific check.
- detect deprecation via description starting with "DEPRECATED"
- keep the other SKILL-06 check (length) and all other rules applying
- add test/test-validate-skills.js + fixtures, wired into npm test
Zied Jlassi