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/SecondarySchoolDetailView.tsx

@@ -110,10 +110,12 @@ export function SecondarySchoolDetailView({
   // Special schools / PRUs / AP sit the same GCSEs but teach pupils with SEND,
   // so their headline attainment is far below the mainstream average by design.
   // Drop the England comparison + "below" framing so the page doesn't portray
-  // them as failing against a benchmark that doesn't fit. (Also guards a
-  // placeholder all-zero Attainment 8.)
+  // them as failing against a benchmark that doesn't fit. Attainment 8 is a
+  // single 0–80 score with no subject breakdown to test for a placeholder, so
+  // this keys off establishment type only — a genuine (if extreme) 0.0 at a
+  // mainstream school still shows its real value and comparison.
   const isSpecial = isSpecialSchool(schoolInfo);
-  const suppressComparison = isSpecial || (latestResults != null && latestResults.attainment_8_score === 0);
+  const suppressComparison = isSpecial;
 
   const admissionsTag = (() => {
     const policy = schoolInfo.admissions_policy?.toLowerCase() ?? '';