feat(foreshadow): 写作台本章伏笔主动提醒（前端）

- 新增 chapterForeshadow 纯分类：按当前章分 可回收/待回收/已逾期（启用闲置的 isWindowApproaching）
- useChapterForeshadow hook（复用 GET /foreshadow，切章仅重分类不重拉）
- 右栏「本章参考」+ ContextDrawer 伏笔页新增「本章伏笔」实时清单，
  分色展示 + 跳看板链接 + 空态；标注『按已验收进度』

apps/web/lib/foreshadow/useChapterForeshadow.ts

@@ -0,0 +1,71 @@
+"use client";
+
+import { useCallback, useEffect, useMemo, useState } from "react";
+
+import { api } from "@/lib/api/client";
+import type { ForeshadowView } from "@/lib/api/types";
+import {
+  classifyChapterForeshadow,
+  type ChapterForeshadowGroups,
+} from "./chapterForeshadow";
+
+// 写作台「本章伏笔」提醒的数据层：拉本项目全量伏笔（GET /foreshadow，只读），
+// 再按当前章号本地分类。项目内一次拉取，切章仅重新分类（不重复请求）。
+export type ChapterForeshadowStatus = "loading" | "ready" | "error";
+
+export interface UseChapterForeshadow {
+  groups: ChapterForeshadowGroups;
+  status: ChapterForeshadowStatus;
+  reload: () => void;
+}
+
+const FORESHADOW_PATH = "/projects/{project_id}/foreshadow" as const;
+const EMPTY_ITEMS: ForeshadowView[] = [];
+
+export function useChapterForeshadow(
+  projectId: string,
+  chapterNo: number,
+): UseChapterForeshadow {
+  const [items, setItems] = useState<ForeshadowView[]>(EMPTY_ITEMS);
+  const [status, setStatus] = useState<ChapterForeshadowStatus>("loading");
+  // reload 触发器：自增即重新拉取。
+  const [nonce, setNonce] = useState(0);
+
+  useEffect(() => {
+    let cancelled = false;
+    setStatus("loading");
+    void (async () => {
+      try {
+        const { data, error } = await api.GET(FORESHADOW_PATH, {
+          params: { path: { project_id: projectId } },
+        });
+        if (cancelled) return;
+        if (error || !data) {
+          setItems(EMPTY_ITEMS);
+          setStatus("error");
+          return;
+        }
+        setItems(data.foreshadow ?? EMPTY_ITEMS);
+        setStatus("ready");
+      } catch {
+        // 网络层失败（后端不可达/CORS）：openapi-fetch 直接抛而非返回 error 信封。
+        if (cancelled) return;
+        setItems(EMPTY_ITEMS);
+        setStatus("error");
+      }
+    })();
+    return () => {
+      cancelled = true;
+    };
+  }, [projectId, nonce]);
+
+  // 切章不重拉，仅重新分类（伏笔窗口相对章号变化）。
+  const groups = useMemo(
+    () => classifyChapterForeshadow(items, chapterNo),
+    [items, chapterNo],
+  );
+
+  const reload = useCallback(() => setNonce((n) => n + 1), []);
+
+  return { groups, status, reload };
+}