Redirect old help article links and 404 pages to the new custom domain landing page

When migrating our help center to Featurebase and setting up a custom domain, our old article links (e.g., organization.featurebase.app/help/article/slug) result in a 404 error.

We need a way to automatically redirect these old URLs to their new counterparts on the Featurebase custom domain to avoid broken links and provide a seamless user experience.