fix(compare): expert should-fixes S1-S4, S6 — banded chips, P8 reason, KS4 gap caption, all-through framing, cohort sizes

S1: first-choice chip banded (More than half / About 1 in 3 / Over 1 in 4
missed out) so a 44%-offered grammar isn't understated by half.
S2: Progress 8 explains its absence for 2024/25+ cohorts (no KS2 baseline,
COVID) instead of a bare 'No data'.
S3: KS4 trend charts get their own honest gap caption (2019/20-2020/21
unpublished; later years not in our dataset yet); y-axis 'Value'→'Score';
buildCompareChart exposes englandOnlyYears.
S4: all-through schools labelled in chips, rail caption says 'N schools ·
<phase> view' for mixed baskets, whole-school roll no longer judged
against the single-phase median, community section carries an all-ages
caveat.
S6 (spec §8.5): disadvantaged attainment shows the cohort behind it
('of ~50 disadvantaged pupils').

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0146VHeLAWjDVE2B5uU67jCB

nextjs-app/components/ComparisonView.tsx

@@ -365,12 +365,18 @@ export function ComparisonView({
             style={{ '--school-count': activeSchools.length } as CSSProperties}
             aria-label="Schools in this comparison"
           >
-            {/* Fills the 200px label rail on desktop (hidden on mobile). */}
+            {/* Fills the 200px label rail on desktop (hidden on mobile).
+                All-through schools must not be miscounted as "primary
+                schools"/"secondary schools" — mixed baskets get "· primary
+                view" phrasing instead. */}
             <div className={styles.barCaption}>
               <span className={styles.barCaptionEyebrow}>Comparing</span>
               <span className={styles.barCaptionCount}>
-                {activeSchools.length} {comparePhase} school
-                {activeSchools.length === 1 ? '' : 's'}
+                {activeSchools.every((sch) =>
+                  sch.phase?.toLowerCase().includes(comparePhase),
+                )
+                  ? `${activeSchools.length} ${comparePhase} school${activeSchools.length === 1 ? '' : 's'}`
+                  : `${activeSchools.length} schools · ${comparePhase} view`}
               </span>
             </div>
             {activeSchools.map((school, index) => (
@@ -390,7 +396,13 @@ export function ComparisonView({
                     <span className={styles.chipNameShort}>{shortName(school.school_name)}</span>
                   </a>
                   <span className={styles.chipMeta}>
-                    {[school.local_authority, school.school_type].filter(Boolean).join(' · ')}
+                    {[
+                      /all.?through/i.test(school.phase ?? '') ? 'All-through' : null,
+                      school.local_authority,
+                      school.school_type,
+                    ]
+                      .filter(Boolean)
+                      .join(' · ')}
                   </span>
                 </span>
                 <button