fix: #3607228 Point the About and Countries call-to-action buttons at real pages

Closes https://www.drupal.org/project/horizonaid/issues/3607228

Four call-to-action buttons in the recipe's default Canvas content had no href, so they rendered as dead links. Each now points at a real page:

About page (content/canvas_page/02-about.yml)

• "Read Our Full Story" -> internal:/impact
• "Learn About Our Approach" -> internal:/programs
• "Explore More" -> internal:/resources

Countries page (content/canvas_page/06-countries.yml)

• "Explore Our Impact" -> internal:/impact

All four targets return HTTP 200 on a live Varbase 11 build, and the three About buttons were verified in a real browser to render with the new hrefs.

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