Refactor schedule functionality in frontend

- Extract schedule logic into custom useSchedule hook
- Update BlocklistScheduleSection to use the new hook
- Add tests for useSchedule hook
- Update documentation with task progress

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

frontend/src/hooks/useSchedule.ts

@@ -2,7 +2,7 @@
  * React hook for fetching and updating the blocklist import schedule.
  */
 
-import { useCallback, useEffect, useState } from "react";
+import { useCallback, useEffect, useRef, useState } from "react";
 import { fetchSchedule, updateSchedule } from "../api/blocklist";
 import { handleFetchError } from "../utils/fetchError";
 import type { ScheduleConfig, ScheduleInfo } from "../types/blocklist";
@@ -12,6 +12,7 @@ export interface UseScheduleReturn {
   loading: boolean;
   error: string | null;
   saveSchedule: (config: ScheduleConfig) => Promise<void>;
+  refresh: () => void;
 }
 
 /**
@@ -21,9 +22,13 @@ export function useSchedule(): UseScheduleReturn {
   const [info, setInfo] = useState<ScheduleInfo | null>(null);
   const [loading, setLoading] = useState(true);
   const [error, setError] = useState<string | null>(null);
+  const abortRef = useRef<AbortController | null>(null);
 
-  useEffect(() => {
+  const refresh = useCallback((): void => {
+    abortRef.current?.abort();
     const controller = new AbortController();
+    abortRef.current = controller;
+
     setLoading(true);
     setError(null);
 
@@ -37,19 +42,24 @@ export function useSchedule(): UseScheduleReturn {
         handleFetchError(err, setError, "Failed to load schedule");
       })
       .finally(() => {
-        if (controller.signal.aborted) return;
-        setLoading(false);
+        if (!controller.signal.aborted) {
+          setLoading(false);
+        }
       });
+  }, []);
+
+  useEffect(() => {
+    refresh();
 
     return (): void => {
-      controller.abort();
+      abortRef.current?.abort();
     };
-  }, []);
+  }, [refresh]);
 
   const saveSchedule = useCallback(async (config: ScheduleConfig): Promise<void> => {
     const updated = await updateSchedule(config);
     setInfo(updated);
   }, []);
 
-  return { info, loading, error, saveSchedule };
+  return { info, loading, error, saveSchedule, refresh };
 }