Add PACKAGES.md analyzing the Lux package ecosystem gaps vs stdlib,
with prioritized implementation plans for markdown, xml, rss, frontmatter,
path, and sitemap packages. Add CLAUDE.md instructions for documenting
Lux language errors in ISSUES.md during every major task.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Adds the post-work checklist (cargo check, cargo test, lux check, lux fmt,
lux lint) and documents all CLI command aliases. Updates test count to 381.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
