SDDS theme must be the default theme for Twig namespaces to work

We may get rid of the components module dependency for the demo, which means this would no longer be an issue, so postponing for now.

Ran into issue trying to get rid of components module so it's a low priority for now.

📌 Reconcile components vs SDC namespaces for SDDS includes/embeds Postponed

This is the components module issue:

🐛 Multiple Active Themes - Only default theme namespaces work after upgrading to v3 Active

I pinged @acbramley to see if he can look at that issue.