copy(web): replace em dashes in public copy

Rewrites every visitor-facing string that used an em dash, choosing the
punctuation for what the dash was doing: a colon before a list or
explanation, a comma for an aside, a full stop between two thoughts,
parentheses for an aside mid-sentence. Covers page titles and meta
descriptions, the home and admissions guide copy, school page headings
and notes, the compare page, metric labels and tooltips.

Two rewrites also fix the sentence around them: the closure banner no
longer repeats "proposed for closure", and the cut-off caveat's list of
priorities now parses.

A lone dash marking a missing value in a table cell stays: it is a data
convention, not prose. A Jest guard walks the source with the TypeScript
parser and fails on any other em dash in a string or JSX text node.

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

nextjs-app/components/compare/CompareCommunity.tsx

@@ -56,12 +56,12 @@ export function CompareCommunity({
       how={
         <>
           The school&apos;s community, from the latest school census. State-school averages are
-          computed from our dataset and shown for context — there&apos;s no &ldquo;right&rdquo;
+          computed from our dataset and shown for context. There&apos;s no &ldquo;right&rdquo;
           number here.
           {anyAllThrough && (
             <>
               {' '}
-              For all-through schools these figures cover the whole school, all ages — not just
+              For all-through schools these figures cover the whole school and all ages, not just
               the {isSecondary ? 'secondary' : 'primary'} phase.
             </>
           )}
@@ -79,7 +79,7 @@ export function CompareCommunity({
           if (pupils != null && capacity != null && capacity > 0) {
             capNote =
               pupils >= capacity
-                ? `${capacity.toLocaleString('en-GB')} places — at or above capacity`
+                ? `${capacity.toLocaleString('en-GB')} places (at or above capacity)`
                 : `of ${capacity.toLocaleString('en-GB')} places (${Math.round((pupils / capacity) * 100)}% full)`;
           }
           return (
@@ -111,7 +111,7 @@ export function CompareCommunity({
         </Measure>
 
         <Measure
-          tip="% of pupils eligible for free school meals — a common measure of how many pupils come from lower-income families. Benchmark computed across state schools in our dataset."
+          tip="% of pupils eligible for free school meals, a common measure of how many pupils come from lower-income families. Benchmark computed across state schools in our dataset."
           label="Free school meals"
         >
         {schools.map((school, i) => {
@@ -145,7 +145,7 @@ export function CompareCommunity({
         </Measure>
 
         <Measure
-          tip="% of pupils receiving SEN support (not including EHC plans). A high figure can mean the school hosts specialist provision — often a strength, not a warning sign. State-school average computed from our dataset."
+          tip="% of pupils receiving SEN support (not including EHC plans). A high figure can mean the school hosts specialist provision, which is often a strength rather than a warning sign. State-school average computed from our dataset."
           label="Extra learning support (SEN)"
         >
         {schools.map((school, i) => {