fix: use sessionStorage instead of query param for logout flag

Logto does exact-match on post_logout_redirect_uri, so ?signed_out
caused "not registered" error. Use sessionStorage flag instead —
set before signOut, read and cleared on LoginPage mount.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ui/src/auth/LoginPage.tsx

@@ -9,10 +9,11 @@ export function LoginPage() {
   const navigate = useNavigate();
   const redirected = useRef(false);
 
-  // Check if we arrived here from a logout redirect
+  // Check if we arrived here from a logout redirect (set by useAuth before signOut)
   const [signedOut] = useState(() => {
-    const params = new URLSearchParams(window.location.search);
+    const flag = sessionStorage.getItem('cameleer:signed_out');
-    return params.has('signed_out');
+    if (flag) sessionStorage.removeItem('cameleer:signed_out');
+    return !!flag;
   });
 
   useEffect(() => {

ui/src/auth/useAuth.ts

@@ -7,7 +7,8 @@ export function useAuth() {
   const { currentTenantId } = useOrgStore();
 
   const logout = useCallback(() => {
-    signOut(window.location.origin + '/platform/login?signed_out');
+    sessionStorage.setItem('cameleer:signed_out', '1');
+    signOut(window.location.origin + '/platform/login');
   }, [signOut]);
 
   return {