docs: overhaul portfolio for monorepo consolidation

- Update stats: 60+ → 275+ repos, MPL-2.0 → PMPL-1.0-or-later
- Replace deleted repo links with current monorepos (polystack,
  nextgen-languages, ipv6-tools, language-bridges, etc.)
- Add new sections: Security, Science (Julia libraries)
- Remove obsolete categories: Zotero, WordPress, SSG (absorbed)
- Update navigation to match new structure

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

Author: Jonathan D.A. Jewell