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/app/compare/page.tsx

@@ -20,8 +20,8 @@ export const metadata: Metadata = {
   keywords: 'school comparison, compare schools, KS2 comparison, primary school performance',
 };
 
-// Force dynamic rendering
-export const dynamic = 'force-dynamic';
+// Dynamic via searchParams; remove force-dynamic so internal data fetches
+// can still use Next.js's per-call revalidate cache.
 
 export default async function ComparePage({ searchParams }: ComparePageProps) {
   const { urns: urnsParam, metric: metricParam } = await searchParams;