feat(auth): use the cookie session and refresh on 401

The token is no longer stored; a tbp_session flag remembers the
login. apiFetch renews the session once on a 401 and sends the
request again. Parallel requests and other tabs share one refresh,
because Auth revokes the session when a refresh token is used twice.
Only a 401 from the refresh ends the session; a 502 or no network
shows the normal error.

src/pages/GameDetail.jsx

@@ -20,7 +20,7 @@ import useSaveAppearance from '../hooks/useSaveAppearance.js';
 import {usePreferences} from '../context/PreferencesContext.jsx';
 import PageContainer from '../components/PageContainer.jsx';
 import {apiFetch} from '../utils/api.js';
-import {getToken} from '../utils/auth.js';
+import {hasSession} from '../utils/auth.js';
 
 const formatUnlockedAt = (instant, locale) => {
     if (!instant) return '';
@@ -45,7 +45,7 @@ export default function GameDetail() {
 
     useEffect(() => {
         let cancelled = false;
-        if (!getToken()) {
+        if (!hasSession()) {
             navigate('/login');
             return;
         }