fix(a11y): WCAG AA colour contrast across every route (P0.1)

Live axe-core inventory found 13 failing fg/bg pairs (3.12:1 coral text/
fills, 4.0-4.5 teal near-misses, 2.7 gold badge, 1.9 chart-colour text).
All replacement values validated ≥4.5:1 against every background they
sit on:

- --accent-coral-dark deepened to #b04a2e and used for coral text roles
  (nav active, back/map links, kickers, chips) and coral fills under
  white text (btn-primary, phase tabs, section-nav compare, chart chips);
  new --accent-coral-darker #9c3f26 for their hovers. Decorative coral
  (pins, bars, borders, focus ring) keeps the brand #e07256.
- --accent-teal darkened to #296f6f (rankings values, metric rows,
  ofsted grades, eyebrows all pass).
- Ofsted green #3c8c3c→#2f7a2f; off-token gold #b8920e→--accent-gold-text.
- Gender-split pink text #b45778→#a04a68; admissions tip numerals to a
  3.8:1 muted brown (28px display text).
- New CHART_TEXT_COLORS: AA-dark counterparts of the Chart.js series
  palette for compare-card values (swatch dots keep true series colour).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

nextjs-app/components/HomeView.module.css

@@ -121,7 +121,7 @@
 
 .viewToggleBtn.active {
   background: var(--bg-card, white);
-  color: var(--accent-coral, #e07256);
+  color: var(--accent-coral-dark, #b04a2e);
   box-shadow: 0 2px 4px rgba(26, 22, 18, 0.08);
 }
 
@@ -222,7 +222,7 @@
 }
 
 .compactItemName:hover {
-  color: var(--accent-coral, #e07256);
+  color: var(--accent-coral-dark, #b04a2e);
 }
 
 .distanceBadge {
@@ -536,7 +536,7 @@
 
 .geoError {
   font-size: 0.8125rem;
-  color: var(--accent-coral, #e07256);
+  color: var(--accent-coral-dark, #b04a2e);
   margin: 0;
   max-width: 340px;
   text-align: center;
@@ -567,9 +567,9 @@
 }
 
 .quickSearchChip:hover {
-  background: var(--accent-coral);
+  background: var(--accent-coral-dark);
   color: white;
-  border-color: var(--accent-coral);
+  border-color: var(--accent-coral-dark);
 }
 
 .exploringRow {
@@ -712,7 +712,7 @@
   font-weight: 700;
   letter-spacing: 0.1em;
   text-transform: uppercase;
-  color: var(--accent-coral, #e07256);
+  color: var(--accent-coral-dark, #b04a2e);
 }
 
 .hiwTitle {
@@ -1062,7 +1062,7 @@
 
 .editorialKicker {
   font-size: 0.68rem;
-  color: var(--accent-coral, #e07256);
+  color: var(--accent-coral-dark, #b04a2e);
   font-weight: 700;
   letter-spacing: 0.1em;
   text-transform: uppercase;
@@ -1300,7 +1300,7 @@
 }
 
 .chipTrackDeadline {
-  color: var(--accent-coral, #e07256);
+  color: var(--accent-coral-dark, #b04a2e);
 }
 
 .chipTrackOffer {