remove copyrighted content and old engram-named binaries

- skill/references/nate-skills-substack-article.md: paid Substack content
- skill/references/claude-skills-guide.md: verbatim Anthropic guide
- skill/dist/engram-*.skill: old project name in binary filenames

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: Paul Kyle