Add emoji toggle setting to parent dashboard Settings panel

Parent can turn the floating school emoji on/off from Settings > Student home screen. Setting persists in the DB and is read via a public /api/public-settings endpoint on the student home page.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

public/app.js

@@ -243,6 +243,10 @@ async function loadHome() {
                  : 'Good evening! 🌙';
   document.querySelector('.subtitle').textContent = greeting;
 
+  const pubSettings = await fetch('/api/public-settings').then((r) => r.json()).catch(() => ({}));
+  document.querySelector('.page-confetti').style.display =
+    pubSettings.show_home_emoji === false ? 'none' : '';
+
   const students = await api('/api/students');
   $('#no-kids').hidden = students.length > 0;
   $('#kid-cards').innerHTML = students