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.module.css

@@ -5,14 +5,14 @@
 }
 
 .container {
-  max-width: 1280px;
+  max-width: 1400px;
   margin: 0 auto;
   padding: 3rem 1.5rem 2rem;
 }
 
 .content {
   display: grid;
-  grid-template-columns: 2fr 1fr 1fr;
+  grid-template-columns: 2fr 1fr;
   gap: 3rem;
   margin-bottom: 3rem;
 }