fix(header): switch to icon-only nav below 823px

src/App.vue

@@ -239,7 +239,7 @@ async function handleLogout() {
   background: var(--ac-header-active-bg);
 }
 
-@media (max-width: 640px) {
+@media (max-width: 823px) {
   .app-header {
     padding: 0 10px;
     gap: 8px;