Review a SKILL.md file for adherence to Anthropic's official agent-skill best practices. Use when the user asks to "review a skill", "check skill quality", "audit skill", "validate skill quality", or before merging a PR that adds or modifies a skill in skills/. Complements the deterministic structural validator (validate_skills.py) by judging content quality — concision, description discoverability, naming, freedom calibration, progressive disclosure.