Add AbortController cleanup to async frontend effects

frontend/src/hooks/useSchedule.ts

@@ -23,16 +23,27 @@ export function useSchedule(): UseScheduleReturn {
   const [error, setError] = useState<string | null>(null);
 
   useEffect(() => {
+    const controller = new AbortController();
     setLoading(true);
-    fetchSchedule()
+    setError(null);
+
+    fetchSchedule(controller.signal)
       .then((data) => {
+        if (controller.signal.aborted) return;
         setInfo(data);
-        setLoading(false);
       })
       .catch((err: unknown) => {
+        if (controller.signal.aborted) return;
         handleFetchError(err, setError, "Failed to load schedule");
+      })
+      .finally(() => {
+        if (controller.signal.aborted) return;
         setLoading(false);
       });
+
+    return (): void => {
+      controller.abort();
+    };
   }, []);
 
   const saveSchedule = useCallback(async (config: ScheduleConfig): Promise<void> => {