Expand to 150+ models, add multi-agent install instructions

- Added 57 new mental models across all categories
- Added 3 new categories: Negotiation, Resilience & Antifragility, Ethics
- Updated README with install instructions for Claude Code, Cursor, Windsurf
- Follows open Agent Skills standard, not Claude Code specific

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>