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/lib/schoolFacts.ts

@@ -7,7 +7,7 @@
  */
 
 import type { School } from './types';
-import { hasNurseryClasses, hasReligiousCharacter, singleSexLabel } from './utils';
+import { hasNurseryClasses, hasReligiousCharacter, isSelective, singleSexLabel } from './utils';
 
 /** The search filter's type groups (backend/school_groups.py), without its
  *  parenthesised notes: fees have a flag of their own. */
@@ -54,7 +54,7 @@ export function schoolFlags(school: FlagFields): SchoolFlag[] {
   const phase = school.phase?.trim().toLowerCase();
 
   if (school.type_group === 'independent') condition('Fee-paying');
-  if (school.admissions_policy?.trim().toLowerCase() === 'selective') condition('Selective');
+  if (isSelective(school.admissions_policy)) condition('Selective');
   const singleSex = singleSexLabel(school.gender);
   if (singleSex) condition(singleSex);
   if (hasReligiousCharacter(school.religious_denomination)) {