feat(lesson-preparation): 中栏纸区容器（正文 + 展开节点 + 右键菜单）

src/modules/lesson-preparation/components/paper-editor/paper-editor.tsx

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+"use client";
+
+import { useMemo, useState } from "react";
+import { useTranslations } from "next-intl";
+import { useLessonPlanEditor } from "../../hooks/use-lesson-plan-editor";
+import { TextbookTiptapEditor } from "./textbook-tiptap-editor";
+import { InlineNode } from "./inline-node";
+import { PaperContextMenu, type ContextMenuState } from "./paper-context-menu";
+import type { LessonPlanNode } from "../../types";
+
+/**
+ * V4 中栏纸区：
+ * - 教材正文 Tiptap 编辑器（max-w-720px 白纸）
+ * - 展开的节点按 order 顺序在段落间插入 inline-node
+ * - 右键菜单（节点操作 / 锚定）
+ *
+ * 注意：V4 的 inline-node 插入位置由节点 order 决定，不由锚点位置决定。
+ * 锚点是正文内的视觉标记，inline-node 是独立块。
+ * 当前实现：所有 inline-node 渲染在正文之后（简化）。
+ * 完整实现需要把正文按段落分割，在段落间插入 inline-node。
+ */
+export function PaperEditor({ readonly }: { readonly?: boolean }) {
+  const t = useTranslations("lessonPreparation");
+  const doc = useLessonPlanEditor((s) => s.doc);
+  const expandedNodeIds = useLessonPlanEditor((s) => s.expandedNodeIds);
+  const [contextMenu, setContextMenu] = useState<ContextMenuState>({
+    visible: false,
+    x: 0,
+    y: 0,
+    nodeId: null,
+    selectionRange: null,
+  });
+
+  const textbookNode = doc.nodes.find((n) => n.type === "textbook_content");
+  const teachingNodes = useMemo(
+    () =>
+      doc.nodes
+        .filter((n): n is LessonPlanNode => n.type !== "textbook_content")
+        .sort((a, b) => a.order - b.order),
+    [doc.nodes],
+  );
+
+  const expandedNodes = useMemo(
+    () => teachingNodes.filter((n) => expandedNodeIds.includes(n.id)),
+    [teachingNodes, expandedNodeIds],
+  );
+
+  if (!textbookNode) {
+    return <div style={{ padding: 48, textAlign: "center", color: "var(--muted-foreground)" }}>No textbook content</div>;
+  }
+
+  const onPaperContextMenu = (e: React.MouseEvent) => {
+    e.preventDefault();
+    const sel = window.getSelection();
+    const hasSelection = sel && sel.toString().length > 0;
+    setContextMenu({
+      visible: true,
+      x: e.clientX,
+      y: e.clientY,
+      nodeId: null,
+      selectionRange: hasSelection ? { from: 0, to: 0 } : null, // 实际偏移由 editor 给
+    });
+  };
+
+  const onInlineNodeContextMenu = (e: React.MouseEvent, nodeId: string) => {
+    e.preventDefault();
+    e.stopPropagation();
+    setContextMenu({
+      visible: true,
+      x: e.clientX,
+      y: e.clientY,
+      nodeId,
+      selectionRange: null,
+    });
+  };
+
+  return (
+    <main
+      style={{
+        overflowY: "auto",
+        padding: "48px 32px 120px",
+        background: "radial-gradient(circle at 50% 0%, rgba(0,0,0,0.015) 0%, transparent 60%), var(--muted)",
+      }}
+      onContextMenu={(e) => {
+        // 默认右键 = 正文右键（锚定菜单）
+        if (!(e.target as HTMLElement).closest("[data-inline-node]")) {
+          onPaperContextMenu(e);
+        }
+      }}
+    >
+      <article
+        style={{
+          background: "var(--lp-paper)",
+          maxWidth: 720,
+          margin: "0 auto",
+          padding: "64px 72px",
+          boxShadow: "var(--lp-paper-shadow)",
+          borderRadius: 2,
+          border: "1px solid var(--lp-paper-edge)",
+          minHeight: 800,
+          fontFamily: "'Fraunces', Georgia, serif",
+          color: "#1a1a1a",
+          lineHeight: 1.7,
+          fontSize: 16,
+        }}
+      >
+        <div
+          style={{
+            fontFamily: "Inter, sans-serif",
+            fontSize: 11,
+            color: "var(--muted-foreground)",
+            letterSpacing: "0.08em",
+            textTransform: "uppercase",
+            marginBottom: 24,
+            paddingBottom: 16,
+            borderBottom: "1px solid var(--border)",
+            display: "flex",
+            justifyContent: "space-between",
+          }}
+        >
+          <span>{t("v4.paper.textbookHeader")}</span>
+          <span>{t("v4.paper.expandedCount", { count: expandedNodes.length })}</span>
+        </div>
+
+        <TextbookTiptapEditor
+          content={(textbookNode as { data: { content: string } }).data.content}
+          readonly={readonly}
+        />
+
+        {/* 展开的节点：按 order 排列在正文之后（简化实现） */}
+        {expandedNodes.map((node) => (
+          <div
+            key={node.id}
+            data-inline-node={node.id}
+            onContextMenu={(e) => onInlineNodeContextMenu(e, node.id)}
+          >
+            <InlineNode node={node} />
+          </div>
+        ))}
+      </article>
+
+      <PaperContextMenu
+        state={contextMenu}
+        onClose={() => setContextMenu((s) => ({ ...s, visible: false }))}
+      />
+    </main>
+  );
+}