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/SecondarySchoolRow.tsx

@@ -11,7 +11,7 @@
 'use client';
 
 import type { School } from '@/lib/types';
-import { buildOfstedListBadge, getPhaseStyle, schoolUrl, formatAgeRange } from '@/lib/utils';
+import { buildOfstedListBadge, getPhaseStyle, schoolUrl, formatAgeRange, isProposedToClose } from '@/lib/utils';
 import styles from './SecondarySchoolRow.module.css';
 
 function detectAdmissionsTag(school: School): string | null {
@@ -97,6 +97,9 @@ export function SecondarySchoolRow({
               {admissionsTag}
             </span>
           )}
+          {isProposedToClose(school) && (
+            <span className={`${styles.provisionTag} ${styles.closingTag}`}>⚠ Proposed to close</span>
+          )}
         </div>
 
         {/* Line 3: KS4 stats */}