boostlook does not support right side ToC

[Becheler]

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.