fix: make inline links visibly accessible

[abrichr]

Summary

• give prose and data links a persistent underline plus explicit visited, hover, and active states
• add a high-contrast global keyboard focus ring and reduced-motion fallback
• preserve the existing quiet treatment for navigation and CTA links
• verify the hierarchy in a real browser at desktop and mobile widths

Why

Inline links such as hello@openadapt.ai depended primarily on color, which made them easy to miss. This introduces a consistent non-color affordance without flattening the site's navigation, buttons, or card hierarchy.

Dependency

This PR is intentionally stacked on #179 (fix/honest-hybrid-positioning) so it does not reintroduce or conflict with the buyer-positioning copy changes.

Validation

• npm test (10 passed)
• npm run build
• npx cypress run --spec cypress/e2e/link-accessibility.cy.js (2 passed)
• desktop and 375px mobile screenshots reviewed