Add all 150 models to SKILL.md index, fix npx install command

- SKILL.md now indexes all models as one-liners across 12 categories
  (was 8 categories with only original models listed)
- Added: psychology, negotiation, learning, game theory, ethics categories
- Existing categories expanded with new models (Chesterton's Fence,
  Lindy Effect, MECE, Planning Fallacy, etc.)
- SKILL.md stays at 321 lines / ~3.5k tokens — well under 500 line limit
- Reference files still only load on-demand for detailed descriptions
- Fixed npx install command: skillsadd → skills add

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