fix: CI validates wrong .md file — should target SKILL.md

[jnMetaCode]

Summary

• CI 每次都失败，原因是 find ... -name '*.md' | head -1 在 Linux 上拿到的不一定是 SKILL.md
• 辅助文件（如 CREATION-LOG.md、code-quality-reviewer-prompt.md）没有 frontmatter，导致 4 个误报
• 修复：直接检查 SKILL.md，如果缺失则报错

Root Cause

# Before: find returns files in inode order on Linux, not alphabetical
SKILL_FILE=$(find "$dir" -maxdepth 1 -name '*.md' | head -1)
# Could return CREATION-LOG.md instead of SKILL.md

# After: always target the canonical skill definition file
SKILL_FILE="${dir}SKILL.md"

Verification

Ran the updated validation logic locally against all 20 skill directories — 20/20 pass, 0 errors.

🤖 Generated with Claude Code