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/components/school/SecondaryHistorySection.tsx

@@ -3,15 +3,11 @@
  * Server component.
  */
 
-import dynamic from 'next/dynamic';
 import type { School, SchoolResult, NationalAverages } from '@/lib/types';
 import { formatPercentage, formatProgress, formatAcademicYear } from '@/lib/utils';
 import { Section, sectionStyles as styles } from './sectionShared';
+import { PerformanceChart } from './charts';
 
-const PerformanceChart = dynamic(
-  () => import('../PerformanceChart').then((m) => m.PerformanceChart),
-  { ssr: false },
-);
 
 export function SecondaryHistorySection({
   yearlyData, schoolInfo, nationalAvg, secondaryAvg, suppressComparison,