style(copy): remove em dashes from the site's prose

The em dash is one of the clearest tells of machine-written text, which
is the exact impression this work exists to remove. Rewritten rather
than substituted: where a dash was carrying a real aside the sentence is
split or recast, not patched with a comma.

Covers the About page, the two Callout labels an editor sees in the
admin panel, and PUBLISHING.md, which defines the house style and should
follow it. The rule is now recorded in that house style and in the
spec's voice rules, so it survives this branch.

Code comments are left alone: they are not copy, and the surrounding
codebase uses the same punctuation throughout.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017YmbBhr8s7GusjDE12hrZM

nextjs-app/app/(frontend)/about/page.tsx

@@ -42,7 +42,7 @@ export default function AboutPage() {
       <div className={styles.prose}>
         <p className={styles.lede}>
           I&apos;m a parent in south-west London. When we started looking at
-          primary schools, I found the information I needed was all published —
+          primary schools, I found the information I needed was all published,
           and almost impossible to hold in one place.
         </p>
 
@@ -68,11 +68,11 @@ export default function AboutPage() {
         </p>
 
         <p>
-          What I do have is the problem itself — I&apos;m going through primary
-          admissions right now — and a working knowledge of data, which is what
-          I do for a living. That combination is enough to take published
-          figures and present them honestly. It is not enough to tell you which
-          school is right for your child, and this site never tries to.
+          What I do have is the problem itself. I&apos;m going through primary
+          admissions right now, and I work with data for a living. That
+          combination is enough to take published figures and present them
+          honestly. It is not enough to tell you which school is right for your
+          child, and this site never tries to.
         </p>
 
         <h2 className={styles.subheading}>Where the numbers come from</h2>
@@ -96,9 +96,10 @@ export default function AboutPage() {
         <p>
           A school is not its results. The figures here describe one year group,
           on a handful of days, measured in a way that suits national statistics
-          rather than your child. A small cohort makes percentages swing wildly
-          — in a class of thirty, one pupil is more than three points. Results
-          say nothing at all about whether a child will be happy somewhere.
+          rather than your child. A small cohort makes percentages swing wildly.
+          In a class of thirty, one pupil is worth more than three points.
+          Results say nothing at all about whether a child will be happy
+          somewhere.
         </p>
 
         <p>
@@ -113,8 +114,8 @@ export default function AboutPage() {
         <h2 className={styles.subheading}>If something&apos;s wrong</h2>
 
         <p>
-          Tell me and I&apos;ll fix it. Genuinely — if a figure looks wrong, or
-          a page gives a misleading impression of a school, I want to know.
+          Tell me and I&apos;ll fix it. If a figure looks wrong, or a page gives
+          a misleading impression of a school, I genuinely want to know.
           It&apos;s the fastest way this gets better.
         </p>