feat(destinations): the post-16 section, replacing the placeholder

The 'Post-16 destination data coming soon' note is deleted rather than
reworded: for a school with no sixth form the truthful statement is that
the question does not apply, and a placeholder there implies something is
missing. hasSixthForm and .sixthFormNote go with it — nothing else used them.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BvdDKvFFSZuMVDH5fEyTob

nextjs-app/components/school/SecondarySchoolSections.tsx

@@ -21,6 +21,7 @@ import type { SecondaryFlags } from '@/lib/schoolSections';
 import { OfstedSection } from './OfstedSection';
 import { GcseSection } from './GcseSection';
 import { DestinationsSection } from './DestinationsSection';
+import { Post16DestinationsSection } from './Post16DestinationsSection';
 import { SecondaryAdmissionsSection } from './SecondaryAdmissionsSection';
 import { DistanceSection } from './DistanceSection';
 import { SecondaryHistorySection } from './SecondaryHistorySection';
@@ -94,6 +95,12 @@ export function SecondarySchoolSections({
         <DestinationsSection destinations={destinations.ks4} />
       )}
 
+      {/* Sixth-form schools only. Absent, not placeheld, for a school with no
+          post-16 provision — the question simply does not apply there. */}
+      {flags.hasKs5Destinations && destinations?.ks5 && (
+        <Post16DestinationsSection destinations={destinations.ks5} />
+      )}
+
       {/* See PrimarySchoolSections: distance and EES admissions are independent
           sources, so either one warrants the section. */}
       {(admissions || admissionDistance) && (
@@ -102,7 +109,6 @@ export function SecondarySchoolSections({
           admissionDistance={admissionDistance}
           admissionsHistory={admissionsHistory}
           schoolInfo={schoolInfo}
-          hasSixthForm={flags.hasSixthForm}
         />
       )}