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/SchoolRow.tsx

@@ -40,12 +40,18 @@ export function SchoolRow({
 
   // Special schools / PRUs / AP: the mainstream RWM measure and its England
   // comparison aren't a fair judgement (their pupils have SEND), so a "0% ·
-  // −62 vs national" row misrepresents them. Treat the mainstream stat as not
-  // comparable — same for a placeholder all-zero value.
+  // −62 vs national" row misrepresents them. Also guard a placeholder all-zero
+  // row (every subject 0 — a special/suppressed signature), matching
+  // SchoolDetailView's ks2Placeholder. 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.
+  const rwmPlaceholder =
+    school.rwm_expected_pct === 0 &&
+    (school.reading_expected_pct ?? 0) === 0 &&
+    (school.writing_expected_pct ?? 0) === 0 &&
+    (school.maths_expected_pct ?? 0) === 0;
   const rwmComparable =
-    school.rwm_expected_pct != null &&
-    school.rwm_expected_pct !== 0 &&
-    !isSpecialSchool(school);
+    school.rwm_expected_pct != null && !rwmPlaceholder && !isSpecialSchool(school);
 
   // vs-national delta
   const rwmDelta =