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/SchoolSearchModal.module.css

@@ -11,7 +11,7 @@
 }
 
 .warning {
-  background: rgba(201, 162, 39, 0.15);
+  background: var(--accent-gold-bg);
   border: 1px solid var(--accent-gold, #c9a227);
   color: var(--text-primary, #1a1612);
   padding: 1rem;
@@ -43,7 +43,7 @@
 .searchInput:focus {
   outline: none;
   border-color: var(--accent-coral, #e07256);
-  box-shadow: 0 0 0 3px rgba(224, 114, 86, 0.15);
+  box-shadow: 0 0 0 3px var(--accent-coral-bg);
 }
 
 .searchSpinner {
@@ -138,30 +138,6 @@
   gap: 0.25rem;
 }
 
-.addButton {
-  padding: 0.625rem 1.25rem;
-  font-size: 0.9rem;
-  font-weight: 600;
-  border: none;
-  border-radius: 8px;
-  cursor: pointer;
-  transition: all 0.2s ease;
-  white-space: nowrap;
-  background: var(--accent-coral, #e07256);
-  color: white;
-}
-
-.addButton:hover:not(:disabled) {
-  background: var(--accent-coral-dark, #c45a3f);
-  transform: translateY(-1px);
-  box-shadow: 0 4px 12px rgba(224, 114, 86, 0.3);
-}
-
-.addButton:disabled {
-  background: var(--bg-secondary, #f3ede4);
-  color: var(--text-muted, #8a847a);
-  cursor: not-allowed;
-}
 
 .noResults {
   text-align: center;