Show the Horizon Aid home page as the site template screenshot in the installer

Problem/Motivation

The site template card in the browser installer shows screenshot.webp, which is currently the Horizon Aid logo on a light background. Next to Varbase Starter, which shows its own artwork, the card gives no idea what the template actually builds, and the picker is the one place where a site builder chooses between templates.

Steps to reproduce

1. Build a Varbase project and require the Horizon Aid site template.
2. Open /core/install.php and look at the "Choose a site template" step.
3. The Horizon Aid card is a logo on white, not a preview of the site.

Proposed resolution

Replace screenshot.webp with a preview of the home page the template actually installs: the header, the hero image and the Focus Forward panel, at the same 632×304 the other site template cards use.

Remaining tasks

• ✅ File an issue about this project
• ❌ Addition/Change/Update/Fix to this project
• ❌ Testing to ensure no regression
• ➖ Automated unit/functional testing coverage
• ➖ Developer Documentation support on feature change/addition
• ➖ User Guide Documentation support on feature change/addition
• ❌ 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

User interface changes

• The Horizon Aid card in the site template picker previews the home page.

API changes

• N/A

Data model changes

• N/A

Release notes snippet

• The site template picker now previews the Horizon Aid home page instead of showing the logo.