fix(search): no LA comparison for independent schools (H2)

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

nextjs-app/lib/utils.ts

@@ -758,6 +758,16 @@ export function isSpecialSchool(school: { school_type?: string | null }): boolea
   return /\bspecial\b/.test(t) || /pupil referral/.test(t) || /alternative provision/.test(t);
 }
 
+/**
+ * Independent (fee-paying) schools: GIAS types "Other independent school" and
+ * "Other independent special school". DfE's Attainment 8 for them leaves out
+ * IGCSEs, and DfE's LA averages cover state-funded schools only, so callers
+ * drop the "vs LA avg" comparison for them (audit H2).
+ */
+export function isIndependentSchool(school: { school_type?: string | null }): boolean {
+  return /\bindependent\b/i.test(school.school_type ?? '');
+}
+
 /**
  * Whether GIAS records a religious character. "None", "Does not apply" and
  * "Not applicable" are the register's ways of saying it has none; the place