feat: M3 — 伏笔账本 + 节奏引擎 + 大纲（含并发记账 bugfix）

- 伏笔账本：纯函数状态机(OPEN/PARTIAL/CLOSED/OVERDUE) + ForeshadowLedger repo；验收后到期扫描(BackgroundTask 自建 session 置 OVERDUE)；登记/状态变更端点
- 节奏 + 三审齐：foreshadow-analyst + pace-checker 并入 LangGraph 并行审(REVIEW_SPECS)，collect 分列落 chapter_reviews(conflicts/foreshadow_sug/pace)，review SSE 加 foreshadow/pace 事件
- 大纲：outliner Agent 产 OutlineResult(含 foreshadow_windows)，POST /outline 逐章 upsert outline 表；GET /foreshadow?status= 看板
- 前端：伏笔四泳道看板(OVERDUE 琥珀) + 大纲编辑器(窗口徽标) + 节奏节拍图(▁▃▅) + 审稿页消费 foreshadow/pace SSE
- bugfix(T3.8)：并行三审共用请求 session 记账触发 'Session is already flushing' → foreshadow/pace 静默丢失；SqlAlchemyLedgerSink.record 改 add-only(靠端点/事务 commit)，加并发回归测试
- M3 E2E：真实 DB + mock 网关零 token 走通 埋设→进展→验收后扫描 OVERDUE→看板 + 大纲含窗口 + 三审齐 SSE/留痕；E2E 暴露并钉住上述 bug
- 门禁绿：mypy 111 / pytest 228(0 xfailed) / alembic 无漂移；前端 gen:api/lint/tsc/vitest 69/build

apps/web/components/foreshadow/KanbanColumn.tsx

@@ -0,0 +1,61 @@
+"use client";
+
+import type { ForeshadowView } from "@/lib/api/types";
+import type { ForeshadowStatus } from "@/lib/foreshadow/board";
+import { ForeshadowCard } from "./ForeshadowCard";
+
+interface KanbanColumnProps {
+  status: ForeshadowStatus;
+  items: ForeshadowView[];
+  busy: boolean;
+  onTransition: (
+    code: string,
+    toStatus: ForeshadowStatus | null,
+    progressNote: string,
+  ) => void;
+}
+
+// 单个状态泳道（UX §6.8）。OVERDUE 列整列琥珀强调（表头 + 卡片）。
+export function KanbanColumn({
+  status,
+  items,
+  busy,
+  onTransition,
+}: KanbanColumnProps) {
+  const overdue = status === "OVERDUE";
+  return (
+    <section
+      className="flex min-w-0 flex-col rounded border border-line bg-bg"
+      aria-label={`${status} 泳道`}
+    >
+      <header
+        className={`flex items-center justify-between rounded-t border-b px-3 py-2 ${
+          overdue
+            ? "border-overdue bg-overdue/10 text-overdue"
+            : "border-line bg-panel text-ink-soft"
+        }`}
+      >
+        <span className="font-mono text-xs font-semibold">
+          {overdue ? "⚠ " : ""}
+          {status}
+        </span>
+        <span className="font-mono text-xs">{items.length}</span>
+      </header>
+      <ul className="flex-1 space-y-2 overflow-auto p-2">
+        {items.length === 0 ? (
+          <li className="px-1 py-3 text-xs text-ink-soft/60">—</li>
+        ) : (
+          items.map((item) => (
+            <ForeshadowCard
+              key={item.code}
+              item={item}
+              overdue={overdue}
+              busy={busy}
+              onTransition={onTransition}
+            />
+          ))
+        )}
+      </ul>
+    </section>
+  );
+}