feat(detail): replace SATs text tables with cascade bar charts, add admissions bar and history accordion

Redesign the School Details page for better parent comprehension:
- New SatsChart component: horizontal cascade bars with ruler scale and
  national average marker (teal/coral palette matching site theme)
- Admissions section: visual progress bar showing 1st-preference demand
  vs available places, colour-coded by oversubscription status
- Historical data: collapse raw year-by-year table behind a disclosure
  element while keeping the performance line chart always visible
- EAL metric: add national average comparison via DeltaChip (backend now
  includes eal_pct in national averages endpoint)
- New formatWithSuppression utility for null/suppressed data handling

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

nextjs-app/components/SatsChart.module.css

@@ -0,0 +1,190 @@
+/* SatsChart — Cascade bar chart for KS2 SATs results */
+
+.container {
+  display: grid;
+  grid-template-columns: repeat(3, 1fr);
+  gap: 2rem;
+}
+
+/* ── Individual subject column ── */
+.subjectChart {
+  position: relative;
+}
+
+.subjectName {
+  font-size: 0.7rem;
+  font-weight: 600;
+  text-transform: uppercase;
+  letter-spacing: 0.08em;
+  color: var(--text-muted, #6d685f);
+  margin-bottom: 0.65rem;
+}
+
+.chartArea {
+  position: relative;
+  padding-bottom: 0.25rem;
+}
+
+/* ── Gridlines ── */
+.gridlines {
+  position: absolute;
+  top: 0;
+  left: 0;
+  right: 0;
+  bottom: 20px;
+  pointer-events: none;
+}
+
+.gridline {
+  position: absolute;
+  top: 0;
+  height: 100%;
+  width: 1px;
+  background: var(--bg-secondary, #f3ede4);
+}
+
+/* ── National average marker ── */
+.natLine {
+  position: absolute;
+  top: 0;
+  height: calc(100% - 20px);
+  width: 1.5px;
+  background: rgba(224, 114, 86, 0.25); /* --accent-coral at 25% */
+  z-index: 2;
+  pointer-events: none;
+}
+
+.natPill {
+  position: absolute;
+  top: -8px;
+  transform: translateX(-50%);
+  background: var(--accent-coral, #e07256);
+  color: #fff;
+  font-size: 0.55rem;
+  font-weight: 700;
+  padding: 0.1rem 0.4rem;
+  border-radius: 4px;
+  white-space: nowrap;
+  z-index: 3;
+  letter-spacing: 0.02em;
+}
+
+/* ── Bar rows ── */
+.barGroup {
+  position: relative;
+  z-index: 1;
+  display: flex;
+  flex-direction: column;
+  gap: 0.5rem;
+  padding-top: 0.9rem;
+}
+
+.barRow {
+  display: flex;
+  align-items: center;
+  gap: 0.5rem;
+}
+
+.bar {
+  height: 22px;
+  border-radius: 6px;
+  position: relative;
+  transition: width 0.8s cubic-bezier(0.25, 0.46, 0.45, 0.94);
+}
+
+.barExpected {
+  background: var(--accent-teal-light, #3a9e9e);
+}
+
+.barExceeding {
+  background: var(--accent-teal, #2d7d7d);
+}
+
+.barLabel {
+  font-size: 0.72rem;
+  font-weight: 600;
+  color: var(--text-primary, #1a1612);
+  white-space: nowrap;
+  flex-shrink: 0;
+  position: relative;
+  z-index: 3;
+}
+
+.barLabelSuffix {
+  font-weight: 400;
+  color: var(--text-muted, #6d685f);
+  font-size: 0.68rem;
+}
+
+/* ── Ruler ── */
+.ruler {
+  position: relative;
+  height: 16px;
+  margin-top: 0.5rem;
+  border-top: 1px solid var(--border-color, #e5dfd5);
+}
+
+.rulerTick {
+  position: absolute;
+  top: 0;
+  width: 1px;
+  height: 4px;
+  background: var(--border-color, #e5dfd5);
+}
+
+.rulerLabel {
+  position: absolute;
+  top: 6px;
+  font-size: 0.5rem;
+  font-weight: 500;
+  color: var(--text-muted, #6d685f);
+  transform: translateX(-50%);
+  letter-spacing: 0.01em;
+  opacity: 0.7;
+}
+
+/* Anchor first/last labels to edges */
+.rulerLabelFirst {
+  transform: translateX(0);
+}
+
+.rulerLabelLast {
+  transform: translateX(-100%);
+}
+
+/* ── Legend ── */
+.legend {
+  margin-top: 1rem;
+  display: flex;
+  gap: 1.25rem;
+  justify-content: center;
+}
+
+.legendItem {
+  display: flex;
+  align-items: center;
+  gap: 0.35rem;
+  font-size: 0.65rem;
+  font-weight: 500;
+  color: var(--text-muted, #6d685f);
+}
+
+.legendSwatch {
+  width: 8px;
+  height: 8px;
+  border-radius: 3px;
+  flex-shrink: 0;
+}
+
+/* ── Responsive ── */
+@media (max-width: 640px) {
+  .container {
+    grid-template-columns: 1fr;
+    gap: 1.5rem;
+  }
+
+  .legend {
+    flex-wrap: wrap;
+    gap: 0.75rem;
+  }
+}