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/SchoolDetailView.tsx

@@ -18,7 +18,7 @@ import type {
   SchoolDeprivation, SchoolFinance, NationalAverages,
 } from '@/lib/types';
 import {
-  formatPercentage, formatProgress, formatAcademicYear,
+  formatPercentage, formatProgress, formatAcademicYear, isProposedToClose,
 } from '@/lib/utils';
 import { DeltaChip } from './DeltaChip';
 
@@ -313,6 +313,13 @@ export function SchoolDetailView({
                 <span className={styles.metaItem}>{schoolInfo.gender}&apos;s school</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}`}