refactor(detail): render sections on the server behind a client shell

page.tsx now composes the sections and passes them through SchoolDetailShell
as children, so ~1,300 lines of static markup stop shipping as client
JavaScript. The shell keeps what is genuinely interactive: back link, header
reveal, hero map, compare CTA, sticky nav and scroll-spy.

The scroll-spy already located sections via document.getElementById, so it
works unchanged against server-rendered children.

Charts needed a client wrapper: next/dynamic with ssr:false is illegal in a
Server Component, so components/school/charts.tsx is the boundary that keeps
Chart.js (64 KB gz) lazy and browser-only.

Measured on this build:
- school route client chunk: 8 KB gz (33 KB raw)
- total static JS across all chunks: 380.6 -> 350.7 KB gz
- section markup is absent from every client chunk ("Got their first choice",
  "Ofsted reports", "Most deprived" etc. all return 0 hits); shell strings
  still present, as expected
- shared baseline unchanged at 172 KB gz -- out of scope, as designed

The 14 characterization tests pass byte-identical to the commit that
introduced them. Only the render helper changed.

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

nextjs-app/__tests__/support/renderSchoolDetail.tsx

@@ -1,38 +1,77 @@
 /**
  * The single seam between the characterization tests and the component tree.
  *
- * Task 7 of the server/client split rewrites the bodies of these functions to
- * render the new shell + server-sections composition. Nothing else in the test
- * suite may change — the characterization assertions passing unmodified across
- * that rewrite is the proof that behaviour was preserved.
- *
- * National averages now arrive as a server-supplied prop rather than a client
- * fetch, so no fetch stub is needed.
+ * This file is the ONLY thing the server/client split was allowed to change.
+ * It now renders the shell + server-sections composition that
+ * app/school/[slug]/page.tsx builds, instead of the old monolithic views.
+ * Every assertion in schoolDetail.characterization.test.tsx is unchanged —
+ * that is the proof the refactor preserved behaviour.
  */
 
 import { render } from '@testing-library/react';
 import type { ReactNode } from 'react';
-import { SchoolDetailView } from '@/components/SchoolDetailView';
-import { SecondarySchoolDetailView } from '@/components/SecondarySchoolDetailView';
 import { ComparisonProvider } from '@/context/ComparisonProvider';
+import { SchoolDetailShell } from '@/components/school/SchoolDetailShell';
+import { PrimarySchoolSections } from '@/components/school/PrimarySchoolSections';
+import { SecondarySchoolSections } from '@/components/school/SecondarySchoolSections';
+import {
+  computeSchoolFlags, buildNavItems,
+  computeSecondaryFlags, buildSecondaryNavItems,
+} from '@/lib/schoolSections';
 import { nationalAveragesFixture } from './schoolFixtures';
 
-// Both views call useComparison(), which throws outside the provider. In the
+// The shell calls useComparison(), which throws outside the provider. In the
 // app this wrapper comes from app/layout.tsx.
 function withProviders(ui: ReactNode) {
   return <ComparisonProvider>{ui}</ComparisonProvider>;
 }
 
 export function renderSchoolDetail(fixture: any) {
+  const flags = computeSchoolFlags(fixture);
+  const navItems = buildNavItems(flags, {
+    ofsted: fixture.ofsted,
+    admissions: fixture.admissions,
+    yearlyDataLength: fixture.yearlyData.length,
+  });
+
   return render(
-    withProviders(<SchoolDetailView {...fixture} nationalAvg={nationalAveragesFixture} />),
+    withProviders(
+      <SchoolDetailShell
+        {...fixture}
+        nationalAvg={nationalAveragesFixture}
+        navItems={navItems}
+      >
+        <PrimarySchoolSections
+          {...fixture}
+          nationalAvg={nationalAveragesFixture}
+          flags={flags}
+        />
+      </SchoolDetailShell>,
+    ),
   );
 }
 
 export function renderSecondarySchoolDetail(fixture: any) {
+  const flags = computeSecondaryFlags(fixture);
+  const navItems = buildSecondaryNavItems(flags, {
+    ofsted: fixture.ofsted,
+    admissions: fixture.admissions,
+    yearlyDataLength: fixture.yearlyData.length,
+  });
+
   return render(
     withProviders(
-      <SecondarySchoolDetailView {...fixture} nationalAvg={nationalAveragesFixture} />,
+      <SchoolDetailShell
+        {...fixture}
+        nationalAvg={nationalAveragesFixture}
+        navItems={navItems}
+      >
+        <SecondarySchoolSections
+          {...fixture}
+          nationalAvg={nationalAveragesFixture}
+          flags={flags}
+        />
+      </SchoolDetailShell>,
     ),
   );
 }