Make hover motion consistent and respect reduced motion

Problem/Motivation

On the Podcasts page, hover states snap or run on mixed timings (0.15s to 0.3s), and the header animates height. With reduced motion on, the image load-in, the search toggle, the share buttons and the header shadow still move.

Steps to reproduce

1. Open /podcasts and hover the footer links, the social icons and a podcast card "View Show".
2. Turn on reduced motion in the OS, reload, and open the header search.

Proposed resolution

• One timing, $transition-base, through a small mixin that also turns motion off under prefers-reduced-motion.
• One transform-only underline sweep for footer links and the podcast card "View Show", the one the footer sitemap menu already uses. Social icons fade on hover.
• Drop the header height transition, and stop the Drimage load-in under reduced motion.

Remaining tasks

• ✅ File an issue
• ✅ Addition/Change/Update/Fix
• ❌ Testing to ensure no regression
• ➖ Automated unit/functional testing coverage
• ➖ Developer Documentation support
• ➖ User Guide Documentation support
• ➖ 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

• Hover underlines sweep in. With reduced motion, nothing moves.