feat(auth): tell the user when the session expired

Every 401 from Auth or Core now goes through useSessionExpired: the login page
says the session expired and returns to the last page after login. App no
longer removes a token that only the browser clock calls expired, so a backend
401 is the one signal. A 403 on the profile now shows an error instead.

src/App.jsx

@@ -13,7 +13,6 @@ import GameDetail from './pages/GameDetail.jsx';
 import AppHeader from './components/AppHeader.jsx';
 import {Toaster} from '@/components/ui/sonner';
 import {TooltipProvider} from '@/components/ui/tooltip';
-import {getValidToken} from './utils/auth.js';
 
 function App() {
     const {t} = useTranslation();
@@ -24,7 +23,9 @@ function App() {
     const location = useLocation();
 
     useEffect(() => {
-        setIsAuthenticated(!!getValidToken());
+        // No local expiry check here: a 401 from the backend ends the session (useSessionExpired), and a browser
+        // clock that runs ahead would otherwise end it silently.
+        setIsAuthenticated(!!localStorage.getItem('tbp_jwt'));
     }, [location]);
 
     const handleLogout = () => {