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/[place]/[phase]/page.tsx

@@ -0,0 +1,63 @@
+/**
+ * Phase variants of a place page.
+ *
+ * Phase is part of the query — "primary schools in beccles", "secondary
+ * schools in brentwood" — not a filter applied afterwards, so each gets its
+ * own indexable path. A place with no schools of the phase has no page: the
+ * per-phase threshold, not an error.
+ */
+import { notFound } from 'next/navigation';
+import type { Metadata } from 'next';
+import { fetchPlace } from '@/lib/places';
+import { fetchNationalAverages } from '@/lib/api';
+import { PlaceView } from '@/components/places/PlaceView';
+import { absoluteUrl } from '@/lib/site';
+
+interface Props { params: Promise<{ place: string; phase: string }> }
+
+export const revalidate = 604800;
+export const dynamicParams = true;
+
+const PHASES = ['primary', 'secondary'] as const;
+type Phase = (typeof PHASES)[number];
+
+const isPhase = (v: string): v is Phase => (PHASES as readonly string[]).includes(v);
+
+async function resolve(slug: string, phase: Phase) {
+  return (await fetchPlace('town', slug, phase))
+    ?? (await fetchPlace('locality', slug, phase));
+}
+
+export async function generateMetadata({ params }: Props): Promise<Metadata> {
+  const { place: slug, phase } = await params;
+  if (!isPhase(phase)) return { title: 'Place Not Found' };
+  const detail = await resolve(slug, phase);
+  if (!detail || detail.schools.length === 0) return { title: 'Place Not Found' };
+
+  const word = phase === 'secondary' ? 'Secondary' : 'Primary';
+  const { name } = detail.place;
+  return {
+    // Not "Ranked": the table is alphabetical, so the word would be a claim
+    // the page does not keep.
+    title: { absolute: `${word} Schools in ${name} | schoolcompare` },
+    description:
+      `Every ${phase} school in ${name}, with results, Ofsted grades and the local `
+      + `average against England.`,
+    alternates: { canonical: absoluteUrl(`/schools/${slug}/${phase}`) },
+  };
+}
+
+export default async function PlacePhasePage({ params }: Props) {
+  const { place: slug, phase } = await params;
+  if (!isPhase(phase)) notFound();
+  const detail = await resolve(slug, phase);
+  if (!detail || detail.schools.length === 0) notFound();
+
+  const national = await fetchNationalAverages().catch(() => null);
+  const englandAverage = phase === 'secondary'
+    ? national?.secondary?.attainment_8_score ?? null
+    : national?.primary?.rwm_expected_pct ?? null;
+
+  return <PlaceView detail={detail} phase={phase}
+    englandAverage={englandAverage} neighbours={[]} />;
+}