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/HomeView.tsx

@@ -128,7 +128,7 @@ export function HomeView({ initialSchools, filters, totalSchools }: HomeViewProp
 
         {hasSearch && resultsView === 'list' && (
           <div className={styles.resultsHeader}>
-            <h2>
+            <h2 aria-live="polite" aria-atomic="true">
               {initialSchools.total.toLocaleString()} school
               {initialSchools.total !== 1 ? 's' : ''} found
             </h2>
@@ -267,13 +267,13 @@ function CompactSchoolItem({ school, onAddToCompare, isInCompare }: CompactSchoo
       </div>
       <div className={styles.compactItemActions}>
         <button
-          className={`${styles.compactBtn} ${isInCompare ? styles.compactBtnActive : ''}`}
+          className={isInCompare ? 'btn btn-active btn-sm' : 'btn btn-secondary btn-sm'}
           onClick={() => onAddToCompare(school)}
         >
-          {isInCompare ? 'Remove' : 'Compare'}
+          {isInCompare ? '✓ Comparing' : '+ Compare'}
         </button>
-        <a href={`/school/${school.urn}`} className={styles.compactBtnSecondary}>
-          Details
+        <a href={`/school/${school.urn}`} className="btn btn-tertiary btn-sm">
+          View
         </a>
       </div>
     </div>