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/AdmissionsView.module.css

@@ -196,7 +196,7 @@
   margin-bottom: 0.15rem;
 }
 
-.chipTrackDeadline { color: var(--accent-coral, #e07256); }
+.chipTrackDeadline { color: var(--accent-coral-dark, #b04a2e); }
 .chipTrackOffer    { color: var(--accent-teal, #2d7d7d); }
 
 .chipTrackDot {
@@ -278,7 +278,7 @@
   font-weight: 700;
   letter-spacing: 0.1em;
   text-transform: uppercase;
-  color: var(--accent-coral, #e07256);
+  color: var(--accent-coral-dark, #b04a2e);
   margin-bottom: 0.35rem;
 }
 
@@ -399,7 +399,7 @@
   margin-bottom: 0.2rem;
 }
 
-.stepDeadline .stepDate { color: var(--accent-coral, #e07256); }
+.stepDeadline .stepDate { color: var(--accent-coral-dark, #b04a2e); }
 .stepOffer    .stepDate { color: var(--accent-teal, #2d7d7d); }
 
 .stepTitle {
@@ -472,7 +472,7 @@
   font-family: var(--font-playfair), 'Playfair Display', serif;
   font-size: 1.75rem;
   font-weight: 700;
-  color: var(--border-color, #e5dfd5);
+  color: #7d766b; /* 3.8:1 on cream — AA large-text for this 28px numeral */
   line-height: 1;
   margin-bottom: 0.6rem;
 }