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/RankingsView.module.css

@@ -69,7 +69,7 @@
 .filterSelect: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);
 }
 
 .filterSelect optgroup {
@@ -275,32 +275,6 @@
   vertical-align: middle;
 }
 
-.addButton {
-  display: inline-flex;
-  align-items: center;
-  padding: 0.5rem 1rem;
-  font-size: 0.875rem;
-  font-weight: 600;
-  border: 1px solid transparent;
-  border-radius: 6px;
-  cursor: pointer;
-  transition: all 0.2s ease;
-  background: var(--accent-coral, #e07256);
-  color: white;
-  box-sizing: border-box;
-}
-
-.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;
-}
 
 /* No Results */
 .noResults {
@@ -382,22 +356,3 @@
   font-style: italic;
 }
 
-.viewButton {
-  display: inline-flex;
-  align-items: center;
-  padding: 0.5rem 1rem;
-  font-size: 0.875rem;
-  font-weight: 500;
-  color: var(--text-secondary);
-  border: 1px solid var(--border-color, #e0ddd8);
-  border-radius: 6px;
-  text-decoration: none;
-  margin-right: 0.375rem;
-  transition: all var(--transition, 0.2s ease);
-  box-sizing: border-box;
-}
-
-.viewButton:hover {
-  background: var(--bg-secondary);
-  color: var(--text-primary);
-}