feat(ui): site-wide UX/UI audit — unified buttons, tokens, accessibility

- Add shared button system (.btn-primary/secondary/tertiary/active) in globals.css
- Replace 40+ hardcoded rgba() values with design tokens across all CSS modules
- Add skip link, :focus-visible indicators, and ARIA landmarks
- Standardise button labels ("+ Compare" / "✓ Comparing") across all components
- Add collapse/minimize toggle to ComparisonToast
- Fix heading hierarchy (h3→h2 in ComparisonView)
- Add aria-live on search results, aria-label on trend SVGs
- Add "Search" nav link, fix footer empty section, unify max-widths
- Darken --text-muted for WCAG AA compliance (4.6:1 contrast ratio)
- Net reduction of ~180 lines through button style deduplication

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

nextjs-app/components/Footer.tsx

@@ -19,14 +19,6 @@ export function Footer() {
             </p>
           </div>
 
-          <div className={styles.section}>
-            <h4 className={styles.sectionTitle}>About</h4>
-            <ul className={styles.links}>
-              <li>
-              </li>
-            </ul>
-          </div>
-
           <div className={styles.section}>
             <h4 className={styles.sectionTitle}>Resources</h4>
             <ul className={styles.links}>