Feature: rebuild the landing page footer with a credits column

[SandObserver]

Summary

• Replace the footer with a two-part layout: logo link, five text links and the legal line on the left, an "Also by SandObserver" credit on the right.
• Link the footer logo to / and give it the header orbit mark, so the header animation code spins it on hover and keyboard focus.
• Show the version as a changelog link in the legal line, keeping class="verbadge" and data-version for check-dist.
• Give the Posteryard credit its own mark with the Posteryard flag animation on hover and keyboard focus.
• Build the copyright year at build time and drop the dot separators, the wordmark image and the unused footer rules.
• On phones, order the footer as logo, links, credit, legal line.

Testing
All green. Checked in Chrome at 1200, 834 and 375 px, with no horizontal overflow; also checked merged with the other two landing page PRs.

Checklist

• npm run build and npm run check both pass.
• Product UI is shown by running or capturing it, never recreated in CSS.
• Any new preview or screenshot carries no private hostnames or real data.
• Visual changes verified in both colour schemes and both docs themes.
• Links to the app repo still resolve.

[cloudflare-workers-and-pages]

Deploying stackyard-docs with    Cloudflare Pages

Latest commit:	9461a33
Status:	✅  Deploy successful!
Preview URL:	https://453a3d6e.stackyard-docs.pages.dev
Branch Preview URL:	https://feat-landing-footer.stackyard-docs.pages.dev

View logs