feat(ui): mark proposed-to-close schools in listings and detail pages

Amber tag in listing rows (option A) and a slim notice strip under the
detail-page header (option E): proposed for closure, formal process not
necessarily started, check with the local authority before applying.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

nextjs-app/components/SecondarySchoolDetailView.tsx

@@ -23,7 +23,7 @@ import type {
   SchoolAdmissions, SenDetail, Phonics,
   SchoolDeprivation, SchoolFinance, NationalAverages,
 } from '@/lib/types';
-import { formatPercentage, formatProgress, formatAcademicYear, formatAgeRange } from '@/lib/utils';
+import { formatPercentage, formatProgress, formatAcademicYear, formatAgeRange, isProposedToClose } from '@/lib/utils';
 import { DeltaChip } from './DeltaChip';
 import { track, getNavigationSource } from '@/lib/analytics';
 import styles from './SecondarySchoolDetailView.module.css';
@@ -237,6 +237,13 @@ export function SecondarySchoolDetailView({
                 </span>
               )}
             </div>
+            {isProposedToClose(schoolInfo) && (
+              <div className={styles.closingStrip} role="note">
+                <strong>⚠ Proposed to close</strong> — this school is proposed for closure,
+                although a formal closure process has not necessarily started. Check with the
+                local authority before applying.
+              </div>
+            )}
             {schoolInfo.address && (
               <p className={styles.address}>
                 {schoolInfo.address}{schoolInfo.postcode && `, ${schoolInfo.postcode}`}