fix: timeout leak in useIdle (#12908)

app/hooks/useIdle.ts

@@ -53,7 +53,16 @@ export default function useIdle(
     events.forEach((eventName) =>
       window.addEventListener(eventName, handleUserActivityEvent)
     );
+
+    // Start the countdown immediately, otherwise the user is never considered
+    // idle unless activity occurs after mount.
+    onActivity();
+
     return () => {
+      handleUserActivityEvent.cancel();
+      if (timeout.current) {
+        clearTimeout(timeout.current);
+      }
       events.forEach((eventName) =>
         window.removeEventListener(eventName, handleUserActivityEvent)
       );