Replaces the iframe-based viewer with a self-contained file where each
page is a <section id="page-N">. Navigation (sidebar, prev/next, arrow
keys, URL hash) scrolls to sections instead of loading separate files.
Added build.py to regenerate index.html from the individual page files.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
