Section cross references are broken

[stevejpurves]

When a cross reference to a section (heading) is made in curvenote the cross reference generation functionality appears to work as expected, and a visible section reference appears, with apparent hover capabilities.

However, the section reference is not functional:

• Clicking on the section reference in the editor or in view mode does nothing
• When exporting to PDF cross references are broken
• When pulling content locally to myst project, we see cross references in the form of {numref} roles but no target id's on the headings
• When running curvenote start all heading cross references appear broken