fix: prevent SSO re-login loop on OIDC logout

Logout now always redirects to /login?local, either via OIDC
end_session or as a direct fallback, preventing prompt=none
auto-redirect from logging the user back in immediately.

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

ui/src/auth/auth-store.ts

@@ -161,6 +161,8 @@ export const useAuthStore = create<AuthState>((set, get) => ({
         post_logout_redirect_uri: postLogoutRedirect,
       });
       window.location.href = `${endSessionEndpoint}?${params}`;
+    } else {
+      window.location.href = `${config.basePath}login?local`;
     }
   },
 }));