Add interactive JavaScript diffeomorphism visualizations

Creates comprehensive web-based visualization system:

🎯 Interactive Features:
- Real-time parameter controls (sigmoid α,β,γ + special horse)
- Live cube→simplex mapping visualization
- Dynamic quality metrics (symmetry, volume, smoothness, coverage)
- Adaptive special horse configuration
- Distribution type selection
- No matplotlib dependency - runs in any browser

📊 Components:
- docs/interactive/diffeomorphism-explorer.html: Main interactive tool
- docs/interactive/index.html: Landing page for all visualization tools
- thurstone/export_data.py: Python→JSON data export utilities
- Example mapping data in docs/interactive/data/

🚀 Benefits:
- Zero dependencies (D3.js via CDN)
- Shareable URLs with parameter states
- Perfect for documentation and exploration
- GitHub Pages ready
- Much more engaging than static matplotlib plots

This makes the diffeomorphism framework truly explorable!

Co-Authored-By: Claude Sonnet 4 <noreply@anthropic.com>

Author: microprediction