feat(footer): add contact email link

No contact route existed anywhere on the site. Add a
contact@schoolcompare.co.uk mailto link in the footer brand column.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

nextjs-app/components/Footer.tsx

@@ -15,8 +15,15 @@ export function Footer() {
           <div className={styles.section}>
             <h3 className={styles.title}>SchoolCompare</h3>
             <p className={styles.description}>
-              Compare primary and secondary schools across England. Free, independent, built on public data.
+              Compare primary and secondary schools across England.
             </p>
+            <a
+              href="mailto:contact@schoolcompare.co.uk"
+              className={styles.link}
+              data-umami-event="contact_email_clicked"
+            >
+              contact@schoolcompare.co.uk
+            </a>
           </div>
 
           <div className={styles.section}>