fix: accept CRLF line endings in frontmatter check

On Windows checkouts (core.autocrlf=true) every SKILL.md ends lines
with CRLF, so the /^---\n/ pattern never matches: all 39 skills are
falsely reported as "Missing YAML Frontmatter" and quality scores
drop below thresholds even though the frontmatter is complete.

Claude-Session: https://claude.ai/code/session_01WxvtAd56PQLSDsGg2n1DAE