fix(auth, pwa): restore api.auth.me, bump PWA cache to v5.3, and fix CEFR CSS styling

app/static/js/modules/api.js

@@ -28,8 +28,11 @@ window.fetch = function(url, options = {}) {
 export const api = {
     // Auth endpoints
     auth: {
+        async me() {
+            return await fetch('/api/me');
+        },
         async check() {
-            const resp = await fetch('/api/me');
+            const resp = await this.me();
             if (resp.ok) {
                 return await resp.json();
             }