Header Newsletter button is non-functional: it has no link destination

Problem/Motivation

The Newsletter button in the site header does nothing when clicked. It renders as a <button> element with no link destination:

<button class="btn btn-accent btn-sm rounded-0 d-inline-flex align-items-center justify-content-center gap-2 fw-bold me-3 mb-3">Newsletter</button>

The component placement in config/canvas.page_region.vartheme_bs5_rightup.header.yml carries a label of Newsletter but no href key, so the button SDC renders a bare button rather than a link.

The destination already exists: the Newsletter Canvas page is shipped by this recipe at content/canvas_page/10-newsletter.yml and is served at /newsletter. The two menu links labelled Newsletter already point at it correctly; only the header call-to-action button does not.

This is the same class of defect that was fixed for the Horizon Aid footer Subscribe button in #3622817.

Steps to reproduce

1. Build a Drupal CMS site and install the RightUp site template:
   

   ddev composer create-project drupal/cms
   ddev composer config minimum-stability dev
   ddev composer require drupal/rightup:1.0.x-dev
   ddev drush si -y ../recipes/rightup

2. Open the front page.
3. Click the green Newsletter button at the top right of the header.
4. Nothing happens. Inspect the element: it is a <button> with no href.

Proposed resolution

Add "href":"/newsletter" to the header button component inputs in config/canvas.page_region.vartheme_bs5_rightup.header.yml, so the button renders as a link to the Newsletter page this recipe already ships.

Remaining tasks

• ✅ File an issue
• ❌ Addition/Change/Update/Fix
• ❌ Testing to ensure no regression
• ➖ Automated unit/functional testing coverage
• ➖ Developer Documentation support
• ➖ User Guide Documentation support
• ➖ UX/UI designer responsibilities
• ➖ Accessibility and Readability
• ❌ Reviewed by a human
• ❌ Code review by maintainers
• ❌ Full testing and approval
• ❌ Credit contributors
• ❌ Review with the product owner
• ❌ Update Release Notes
• ❌ Release

Release notes snippet

• fix: Give the header Newsletter button a link destination. It rendered as a button with no target, so the header newsletter call to action did nothing when clicked.