feat(school-detail): editorial hero with signal chips, at-a-glance stats, summary

Elevates the primary school detail hero from a flat report header into a
scannable editorial block. Parents can read the headline signal in seconds.

- A1: bump .schoolName to clamp(2rem, 5vw, 3.25rem) Playfair.
- A2: framework-aware signal chip strip via new buildOfstedHeroChip() helper.
  Branches on ofsted.framework so Report Card schools never show a fake
  overall grade — they get "Ofsted Report Card" + inspection date +
  Safeguarding: Met/Not met. OEIF schools keep the grade word.
- A3: oversized Playfair stats — Reading, Writing & Maths % (primary) or
  Attainment 8 (secondary) with inline DeltaChip vs national, Ofsted
  verdict with tone colouring, and first-choice offer rate.
- B1: italic serif one-sentence summary via buildSchoolSummary() helper,
  also framework-aware so Report Card schools are described by framework,
  not a synthetic grade.
- C1: new DeltaChip component reused in the two headline KS2 metric cards
  (rwm_expected_pct, rwm_high_pct).

All copy uses "Reading, Writing & Maths" in full. Secondary detail view
untouched in this slice.

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

nextjs-app/components/DeltaChip.tsx

@@ -0,0 +1,57 @@
+/**
+ * DeltaChip — small coloured chip showing how a value compares to a baseline.
+ *
+ * Example: <DeltaChip value={70} baseline={60} unit="pts" />  →  "+10 pts"
+ *
+ * Colours (reuse globals.css status tokens):
+ *   above baseline  → statusGood   (teal)
+ *   below baseline  → statusBad    (coral)
+ *   within ±tolerance → statusWarn (gold, "in line")
+ */
+
+import styles from './DeltaChip.module.css';
+
+interface DeltaChipProps {
+  value: number | null | undefined;
+  baseline: number | null | undefined;
+  /** Unit suffix for the delta (e.g. "pts", "%") */
+  unit?: string;
+  /** Absolute delta below which the chip is treated as neutral */
+  tolerance?: number;
+  /** Override label when we want "vs national" under a number */
+  suffix?: string;
+  /** Smaller variant for inline use next to metric values */
+  size?: 'sm' | 'md';
+}
+
+export function DeltaChip({
+  value,
+  baseline,
+  unit = 'pts',
+  tolerance = 1,
+  suffix,
+  size = 'md',
+}: DeltaChipProps) {
+  if (value == null || baseline == null) return null;
+
+  const delta = value - baseline;
+  const rounded = Math.round(delta);
+
+  let tone: 'good' | 'bad' | 'neutral';
+  if (Math.abs(delta) < tolerance) tone = 'neutral';
+  else if (delta > 0) tone = 'good';
+  else tone = 'bad';
+
+  const toneClass =
+    tone === 'good' ? styles.good : tone === 'bad' ? styles.bad : styles.neutral;
+
+  const sign = rounded > 0 ? '+' : '';
+  const label = `${sign}${rounded} ${unit}`.trim();
+
+  return (
+    <span className={`${styles.chip} ${toneClass} ${size === 'sm' ? styles.sm : ''}`}>
+      {label}
+      {suffix && <span className={styles.suffix}>{suffix}</span>}
+    </span>
+  );
+}