boostlook does not support right side ToC

## On the PR branch

I added support for intra-page navigation:

https://517.graph.prtest3.cppalliance.org/graph/primitives.html

## On the develop preview

This ToC disappears, as well as our warning banner:

https://www.boost.org/doc/libs/develop/doc/antora/graph/primitives.html

## Why it matters

This is problematic as several users asked us for this page navigation.
Also some pages are fairly long and scrolling is a no-go.

Compare the linked PR-branch preview with the develop preview, then inspect boostlook's CSS layout for the Antora page navigation and warning banner. Confirm the change in the develop preview: the right-side ToC and warning banner should both remain visible on long documentation pages.

Written by the indexing model from the issue text.