* docs: migrate install guides to brew/script-first, keep npm (CUE-504)
* docs: keep README install simple (npm only), link to full guide
* docs: use script install in README (no Node.js dependency)
* docs: split Installation into sub-headings per platform
- Add introduction page with demo video, Why Actionbook section, and How It Works steps
- Configure Mintlify theme with black/white color scheme
- Add Actionbook logo (light/dark variants)
- Set up navigation structure with Documentation and API Reference tabs
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>