Fix docsite sidebar navigation by using Html.Unsafe.data for script content
Html.txt HTML-encodes its content, turning quotes into " inside
<script> tags. This made window.BASE_URL undefined (invalid JS),
causing the sidebar to fall back to './' and produce doubled paths
like odoc-interactive-extension/odoc-interactive-extension/demo1.html.
Use Html.Unsafe.data instead, which outputs raw content appropriate
for script tags.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>