fix: #3622817 Footer Subscribe button is non-functional: it has no link destination

Fixes #3622817.

What this changes

The footer "Join Our Mission" Subscribe button was placed with no href input, so the Button component rendered a bare <button type="button"> with no behaviour attached. Clicking it as an anonymous visitor did nothing at all.

One line in config/canvas.page_region.vartheme_bs5_horizonaid.footer.yml gives it the destination it was missing:

"label":"Subscribe","href":"/form/newsletter-subscribe","target":"self"

It points at the Newsletter Subscribe webform that Varbase already provides through varbase_webform_base, so nothing new is added and there is no new dependency.

Why a link and not an embedded form

Two reasons.

The Horizon Aid stylesheet specifies a Subscribe button in the footer, not an inline email field, so a link keeps the design intent.

Embedding the webform in the footer also does not work. A form rendered inside a Canvas SDC section cannot complete its submit cycle: the response it needs to send is wrapped by Twig into a RuntimeError before RenderSafeComponentContainer can re-throw it, so the submission is saved but the visitor sees nothing. Linking to the form avoids that entirely.

Verification

Anonymous, on a Horizon Aid site built from this recipe:

• The footer renders <a href="/form/newsletter-subscribe" class="btn btn-accent ..."> instead of a bare button.
• Clicking it reaches the Newsletter Subscribe form.
• Submitting records the subscription, and the confirmation is visible in the viewport.
• The button's appearance is unchanged.

Note that the defect is not visible in a screenshot: a <button> and an <a> with the same classes render pixel for pixel identically.

Checkpoints:

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

AI-Generated: Yes