Adds `skill-manifest` command that scans a skills directory, extracts
frontmatter and trigger conditions from each SKILL.md, and outputs a
compact JSON manifest. This reduces per-agent skill discovery from 36
Read operations (~6,000 tokens) to a single manifest read (~1,000 tokens).
Closes#1976
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>
