fix(school): send the school page its admissions policy, and read it exactly

The header's Selective flag read school_info.admissions_policy, which the
detail endpoint never sent, so no school page could flag Selective while
its search row did (staging E2E: The Grammar School at Leeds). The detail
payload now carries it, and a contract test checks it carries every field
the header's flags read.

Sending it would have switched on two older copies of the tag logic #176
fixed in the rows. The Admissions section and the cut-off note both tested
includes('selective'), so every non-selective secondary would have read
"entry is by selective examination". The section also counted "None" as a
faith: Burntwood reads "a faith-based admissions priority (None)" today.
All of them now share isSelective() and hasReligiousCharacter(), which also
treats "Not applicable" as no faith, as the place table already does.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

nextjs-app/__tests__/lib/schoolFacts.test.ts

@@ -59,6 +59,8 @@ describe('schoolFlags', () => {
   it('never prints Non-selective, and never a no-faith value', () => {
     expect(labels({ admissions_policy: 'Non-selective', religious_denomination: 'Does not apply' })).toEqual([]);
     expect(labels({ admissions_policy: 'Not applicable', religious_denomination: 'None' })).toEqual([]);
+    // PlaceView's rule: GIAS sometimes says "Not applicable" for no faith too.
+    expect(labels({ religious_denomination: 'Not applicable' })).toEqual([]);
   });
 
   it('prints the religious character as the register records it', () => {