fix(detail): filter Ofsted sentinel codes, show sixth-form judgement, label carried-forward grades

Batch A of applying compare-screen learnings to the detail page (points 2-3):

- Point 2: the legacy OEIF sub-judgement grid rendered any non-null value
  via OFSTED_LABELS[value], so Ofsted's sentinel code 9 ('not applicable')
  leaked as an undefined label, and the sixth-form judgement was dropped
  entirely. New shared ofstedLegacyAreas() helper returns only real grades
  (1-4) and includes Sixth Form provision. Both detail views + the
  all-same-grade check use it.
- Point 3: the OEIF disclaimer always claimed 'Ofsted no longer makes an
  overall judgement' even when showing a carried-forward grade. It's now
  grade_source-aware and labels carried-forward grades as such, matching
  the compare screen.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0146VHeLAWjDVE2B5uU67jCB

nextjs-app/lib/utils.ts

@@ -680,6 +680,42 @@ export function buildSchoolSummary(
   return parts.join(', ') + '.';
 }
 
+// ─── Legacy (OEIF) sub-judgement areas ────────────────────────────────────────
+
+export interface OfstedLegacyArea {
+  label: string;
+  value: number;
+}
+
+/**
+ * The published OEIF sub-judgement areas for the legacy Ofsted layout, in
+ * display order. Only real grades (1–4) are returned: Ofsted's sentinel
+ * codes for "not applicable / no judgement" (9, and any 0/8 variants) and
+ * nulls are filtered out, so a cryptic "9" never renders as a rating.
+ * Sixth Form provision is included where a school has one — it was
+ * previously dropped from the detail grid entirely.
+ */
+export function ofstedLegacyAreas(ofsted: {
+  quality_of_education?: number | null;
+  behaviour_attitudes?: number | null;
+  personal_development?: number | null;
+  leadership_management?: number | null;
+  early_years_provision?: number | null;
+  sixth_form_provision?: number | null;
+}): OfstedLegacyArea[] {
+  const candidates: Array<[string, number | null | undefined]> = [
+    ['Quality of Teaching', ofsted.quality_of_education],
+    ['Behaviour in School', ofsted.behaviour_attitudes],
+    ["Pupils' Wider Development", ofsted.personal_development],
+    ['School Leadership', ofsted.leadership_management],
+    ['Early Years (Reception)', ofsted.early_years_provision],
+    ['Sixth Form', ofsted.sixth_form_provision],
+  ];
+  return candidates
+    .filter((c): c is [string, number] => c[1] != null && c[1] >= 1 && c[1] <= 4)
+    .map(([label, value]) => ({ label, value }));
+}
+
 // ─── List-level Ofsted badge ──────────────────────────────────────────────────
 
 export interface OfstedListBadge {