perf: cache aggressively and trim client bundle

Frontend
- Dynamic-import Chart.js components on detail/compare views so Chart.js
  no longer ships in initial JS.
- Drop force-dynamic on home, compare, rankings so internal data fetches
  reuse Next.js's per-call revalidate cache.
- Switch /school/[slug] to ISR with a 7-day revalidate window (school
  data updates annually).
- Preconnect to analytics + postcodes.io; remove redundant defer on the
  Umami Script tag (afterInteractive already covers it).
- Bump images.minimumCacheTTL to 1 year.
- Extract HowItWorks and Editorial sections as server components passed
  to HomeView via slot props so their JSX stays out of the client bundle.

Backend
- Add GZipMiddleware (min 512 bytes).
- Add CacheAndETagMiddleware: per-path Cache-Control with long s-maxage
  + stale-while-revalidate, ETag generation, and 304 on If-None-Match.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

nextjs-app/components/SecondarySchoolDetailView.tsx

@@ -8,10 +8,15 @@
 
 import { useEffect, useState } from 'react';
 import { useRouter } from 'next/navigation';
+import dynamic from 'next/dynamic';
 import { useComparison } from '@/hooks/useComparison';
-import { PerformanceChart } from './PerformanceChart';
 import { MetricTooltip } from './MetricTooltip';
 import { SchoolMap } from './SchoolMap';
+
+const PerformanceChart = dynamic(
+  () => import('./PerformanceChart').then((m) => m.PerformanceChart),
+  { ssr: false },
+);
 import type {
   School, SchoolResult, AbsenceData,
   OfstedInspection, OfstedParentView, SchoolCensus,