Add registration fallback link

[jamesnw]

Description

Adds a fallback registration link until the Tito Widget is fully loaded.

Steps to test/reproduce

1. Go to Registration page - https://deploy-preview-627--oddleventy.netlify.app/workshops/cascading-layouts/
2. Enable Throttling in your Network dev tools
3. Load the registration page, see there is a Registration link that gets removed once the widget is fully loaded.

[github-actions]

View diff of compiled files (may take a few minutes): https://github.com/oddbird/oddleventy-built/compare/main..registration-fallback

[mirisuzanne]

lgtm!