Add docsite shell plugin and expose structured sidebar data
Extend the odoc shell plugin interface with a sidebar_data field that
provides the raw Odoc_document.Sidebar.t alongside the pre-rendered HTML
sidebar. This allows shell plugins to generate custom sidebar UIs from
structured data rather than being limited to the default HTML rendering.
Create the odoc-docsite shell plugin (--shell docsite) that generates a
docs.rs-inspired documentation website with a fixed header, interactive
sidebar with package selector, full-text search, SPA navigation, dark
mode, and responsive layout. The sidebar JSON is embedded inline in each
page for client-side rendering.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>