fix(review): don't suppress a genuine mainstream 0 in the rows

Review feedback: the rankings/search rows treated any exactly-0 attainment as
not comparable regardless of school type, so a genuine 0 at a mainstream
school rendered as "—" (looks like missing data) and dropped its delta —
stricter and inconsistent with SchoolDetailView's placeholder check.

- SchoolRow: match SchoolDetailView's ks2Placeholder signature — suppress only
  when ALL of RWM + reading + writing + maths are 0 (special/suppressed
  signature), not on a bare rwm === 0. A genuine 0% combined (some pupils met
  individual subjects but not all three) is not all-zero, so it stays
  comparable and shows its real figure + trend.
- SecondarySchoolRow: Attainment 8 is a single 0–80 score with no subject
  breakdown to form an all-zero signature, so key off establishment type only
  (drop the bare att8 === 0 guard). A genuine (if extreme) 0.0 shows its value
  + LA delta.
- For consistency, apply the same to the detail views: drop the bare
  attainment_8_score === 0 guard (KS4 keys off isSpecial only); KS2 keeps the
  all-four-subjects-zero placeholder signature.

Special schools / PRUs / AP are still handled via isSpecialSchool everywhere.
tsc clean; 108/108 unit.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0146VHeLAWjDVE2B5uU67jCB

nextjs-app/components/SchoolDetailView.tsx

@@ -237,19 +237,22 @@ export function SchoolDetailView({
   // reach the mainstream "expected standard", so a 0% headline and an England
   // comparison portray them as failing against a benchmark that doesn't fit.
   const isSpecial = isSpecialSchool(schoolInfo);
-  // Belt-and-braces: a whole-row zero attainment (special or suppressed cohort)
-  // is a placeholder, not a real mainstream result — suppress its comparison
-  // too. A single 0 (e.g. 0% exceeding at a normal school) stays comparable.
+  // Belt-and-braces for KS2: a whole-row zero attainment (every subject 0 — a
+  // special/suppressed signature) is a placeholder, not a real result. This
+  // needs ALL of RWM + reading + writing + maths to be 0, so a genuine 0%
+  // combined (some pupils met individual subjects but not all three) stays
+  // comparable. Attainment 8 is a single 0–80 score with no subject breakdown
+  // to form such a signature, so KS4 keys off establishment type only — a
+  // genuine (if extreme) 0.0 still shows its real figure and comparison.
   const ks2Placeholder = latestResults != null
     && latestResults.rwm_expected_pct === 0
     && (latestResults.reading_expected_pct ?? 0) === 0
     && (latestResults.writing_expected_pct ?? 0) === 0
     && (latestResults.maths_expected_pct ?? 0) === 0;
-  const ks4Placeholder = latestResults != null && latestResults.attainment_8_score === 0;
   // Whether to drop the England-average deltas / national markers / "below"
   // framing on the attainment measures.
   const suppressKs2Comparison = isSpecial || ks2Placeholder;
-  const suppressKs4Comparison = isSpecial || ks4Placeholder;
+  const suppressKs4Comparison = isSpecial;
 
   // Build section nav items dynamically — only sections with data.
   // Order is engagement-led (from section_nav_used analytics): the most-sought