add admin nav link

public/js/nav.js

@@ -0,0 +1,18 @@
+document.addEventListener('DOMContentLoaded', async () => {
+    const adminLink = document.getElementById('admin-link');
+    if (adminLink === null) {
+        return;
+    }
+
+    const response = await fetch('/api/auth/me', {
+        credentials: 'same-origin',
+    });
+    if (!response.ok) {
+        return;
+    }
+
+    const body = await response.json();
+    if (body.user && body.user.isAdmin === true) {
+        adminLink.hidden = false;
+    }
+});