Accessibility improvements across the marketing site

A focused accessibility pass touched the marketing site's navigation, hero, and shared layout components. Several audit findings that had been quietly racking up are now cleared:

• Contrast. Muted text colours bumped up to clear WCAG AA against the page background.
• Focus visibility. Keyboard focus styles restored across navigation links and buttons, so tab navigation makes sense without a mouse.
• Semantic landmarks. Header, main and footer regions declared with proper landmark roles for screen reader navigation.
• Reduced motion. Animations respect prefers-reduced-motion, so visitors who opt out of motion get a calmer page.

Accessibility is mostly invisible when it works correctly, and very visible when it does not. The marketing site is much closer to invisible now.