refactor(app): move site routes into a (frontend) route group

Payload's admin panel ships its own root layout rendering html/body.
Next allows multiple root layouts only when no app/layout.tsx exists, so
the site's routes move into their own group. Route groups are invisible
to routing: every public URL is unchanged, verified against the build's
route table.

The metadata file conventions deliberately stay at the app/ root. Moving
them into the group renamed /icon.png to /icon-4usi79.png (likewise
apple-icon and opengraph-image) and dropped /robots.txt altogether,
which would have broken the /icon.png cache-control rule, the
outputFileTracingIncludes entry for the share card, and robots.txt.

darkThemeSafety reads app/globals.css off disk rather than importing it,
so it needed its own path fix — a grep for import specifiers misses it,
and it fails as an unrunnable suite rather than a failed assertion.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017YmbBhr8s7GusjDE12hrZM

nextjs-app/app/(frontend)/schools/near/[outcode]/page.tsx

@@ -0,0 +1,62 @@
+/**
+ * Postcode district pages.
+ *
+ * No phase variants: nobody searches "primary schools in SW11", so the
+ * variants would be pages without demand. These exist to catch
+ * "schools near <postcode>" and to give London districts a geographic page
+ * where the GIAS town field cannot.
+ */
+import { notFound } from 'next/navigation';
+import type { Metadata } from 'next';
+import { fetchPlace, fetchPlaces } from '@/lib/places';
+import { fetchNationalAverages } from '@/lib/api';
+import { PlaceView } from '@/components/places/PlaceView';
+import { absoluteUrl } from '@/lib/site';
+
+interface Props { params: Promise<{ outcode: string }> }
+
+export const revalidate = 604800;
+export const dynamicParams = true;
+
+export async function generateStaticParams(): Promise<Array<{ outcode: string }>> {
+  // 1,760 of these; same CI budget argument as the town routes.
+  if (process.env.PRERENDER_PLACES !== '1') return [];
+  try {
+    return (await fetchPlaces())
+      .filter((p) => p.kind === 'outcode')
+      .map((p) => ({ outcode: p.slug }));
+  } catch (error) {
+    console.warn('generateStaticParams: API unreachable, falling back to on-demand ISR.', error);
+    return [];
+  }
+}
+
+export async function generateMetadata({ params }: Props): Promise<Metadata> {
+  const { outcode } = await params;
+  const detail = await fetchPlace('outcode', outcode);
+  if (!detail) return { title: 'Place Not Found' };
+
+  const { name, count } = detail.place;
+  return {
+    title: { absolute: `Schools near ${name} | schoolcompare` },
+    description:
+      `${count} schools in the ${name} postcode district, with results, Ofsted grades `
+      + `and how close you had to live to get a place.`,
+    alternates: { canonical: absoluteUrl(`/schools/near/${outcode}`) },
+  };
+}
+
+export default async function OutcodePage({ params }: Props) {
+  const { outcode } = await params;
+  const detail = await fetchPlace('outcode', outcode);
+  if (!detail) notFound();
+
+  const national = await fetchNationalAverages().catch(() => null);
+  return (
+    <PlaceView
+      detail={detail}
+      englandAverage={national?.primary?.rwm_expected_pct ?? null}
+      neighbours={[]}
+    />
+  );
+}