refactor(detail): extract sections as server components

Moves ~1,300 lines of section markup out of the two client views into
components/school/, mirroring the components/compare/ layout. Twelve section
components plus shared primitives, all server components. The only client
file is AdmissionsViewToggle, which owns the hidden/aria-pressed state and
receives both views as server-rendered children.

JSX was extracted mechanically rather than retyped, so the markup the CSS
modules depend on is verbatim.

Sharing follows measured similarity, not assumption:
- Finances (91%) shared. The secondary premises-cost card is gated behind a
  prop so primary pages are unchanged; enabling it is a one-line follow-up.
- Ofsted (80%) shared, but behind a variant prop. The headline similarity hid
  a real fork: on a school with no overall grade the primary page shows a
  "Not rated" badge while the secondary shows a four-area OEIF panel, and the
  disclaimer copy differs. Both preserved exactly; reconciling them is a
  human decision, not a side effect of a move.
- Admissions (14%) and History (40%) kept separate.

Not yet wired up -- the old views still render.

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

nextjs-app/components/school/LocalAreaSection.tsx

@@ -0,0 +1,41 @@
+/**
+ * LocalAreaSection — IDACI deprivation decile. Primary pages only.
+ *
+ * Server component.
+ */
+
+import type { SchoolDeprivation } from '@/lib/types';
+import { MetricTooltip } from '../MetricTooltip';
+import { Section, sectionStyles as styles } from './sectionShared';
+
+// Moved with this section from SchoolDetailView, its only consumer.
+function deprivationDesc(decile: number) {
+  if (decile <= 3) return `This school is in one of England's most deprived areas (decile ${decile}/10). Many pupils may face additional challenges at home.`;
+  if (decile <= 7) return `This school is in an area with average levels of deprivation (decile ${decile}/10).`;
+  return `This school is in one of England's less deprived areas (decile ${decile}/10).`;
+}
+
+export function LocalAreaSection({ deprivation }: { deprivation: SchoolDeprivation }) {
+  return (
+    <Section id="local-area">
+      <h2 className={styles.sectionTitle}>
+        Local Area Context
+        <MetricTooltip metricKey="idaci_decile" />
+      </h2>
+      <div className={styles.deprivationDots}>
+        {Array.from({ length: 10 }, (_, i) => (
+          <div
+            key={i}
+            className={`${styles.deprivationDot} ${i < deprivation.idaci_decile! ? styles.deprivationDotFilled : ''}`}
+            title={`Decile ${i + 1}`}
+          />
+        ))}
+      </div>
+      <div className={styles.deprivationScaleLabel}>
+        <span>Most deprived</span>
+        <span>Least deprived</span>
+      </div>
+      <p className={styles.deprivationDesc}>{deprivationDesc(deprivation.idaci_decile!)}</p>
+    </Section>
+  );
+}