feat(lesson-preparation): 备课模块审计重构 — 跨模块解耦 + i18n + 纯函数抽取 + 错误边界

P0-1 跨模块直查修复：publish-service 不再直查 examQuestions 表，新增 exams/data-access.addExamQuestions 接口，复用 classes/data-access.getStudentIdsByClassIds

P0-2 i18n 接入：新增 zh-CN/en 翻译文件，注册 lessonPreparation 命名空间，17 个组件改造为 useTranslations/getTranslations

P1 纯函数抽取：lib/document-migration.ts（类型守卫替代 as 断言）、lib/node-summary.ts（翻译函数注入）、lib/rf-mappers.ts

P1 错误边界+骨架屏：新增 LessonPlanErrorBoundary 和 4 个 Skeleton 组件

P1 Block 注册表：新增 config/block-registry.tsx（BlockRenderer 组件），node-edit-panel 重构为配置驱动渲染

P1 其他修复：exercise-block 改用 router.refresh()，node-editor/lesson-node 复用 lib/ 纯函数

架构图同步：更新 004 和 005 文档

Refs: docs/architecture/audit/lesson-preparation-audit-report.md

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

@@ -1,6 +1,7 @@
 "use client";
 
 import { useCallback, useMemo } from "react";
+import { useTranslations } from "next-intl";
 import {
   ReactFlow,
   Background,
@@ -11,48 +12,33 @@ import {
   type NodeChange,
   type EdgeChange,
   type Connection,
-  applyNodeChanges,
   applyEdgeChanges,
   BackgroundVariant,
 } from "@xyflow/react";
 import "@xyflow/react/dist/style.css";
 import { useLessonPlanEditor } from "../hooks/use-lesson-plan-editor";
 import { LessonNode } from "./nodes/lesson-node";
+import { toRfNodes, toRfEdges } from "../lib/rf-mappers";
 import type { LessonPlanNode } from "../types";
 
 const nodeTypes = { lesson: LessonNode };
 
-interface Props {
-  textbookId?: string;
-  chapterId?: string;
-  classes?: { id: string; name: string }[];
-}
+// NodeEditor 只负责画布交互，内容编辑由 NodeEditPanel 处理
+type Props = Record<string, never>;
 
-export function NodeEditor({ textbookId, chapterId, classes }: Props) {
+export function NodeEditor({}: Props) {
+  const t = useTranslations("lessonPreparation");
   const { doc, selectedNodeId, updateNodePosition, removeNode, connect, selectNode, setEdges } =
     useLessonPlanEditor();
 
-  // 我们的 nodes → React Flow nodes
+  // 使用纯函数映射 nodes/edges
   const rfNodes: Node[] = useMemo(
-    () =>
-      doc.nodes.map((n) => ({
-        id: n.id,
-        type: "lesson",
-        position: n.position,
-        data: n as unknown as Record<string, unknown>,
-        selected: n.id === selectedNodeId,
-      })),
+    () => toRfNodes(doc.nodes, selectedNodeId),
     [doc.nodes, selectedNodeId],
   );
 
-  // edges 直接兼容
   const rfEdges: Edge[] = useMemo(
-    () =>
-      doc.edges.map((e) => ({
-        ...e,
-        animated: true,
-        style: { stroke: "#1976d2", strokeWidth: 2 },
-      })),
+    () => toRfEdges(doc.edges),
     [doc.edges],
   );
 
@@ -60,15 +46,16 @@ export function NodeEditor({ textbookId, chapterId, classes }: Props) {
     (changes: NodeChange[]) => {
       changes.forEach((change) => {
         if (change.type === "position" && change.position) {
-          updateNodePosition(change.id, change.position);
+          // 拖拽结束时（dragging: false）才写入最终位置，避免中间状态污染（修复 P1-1）
+          if (change.dragging === false) {
+            updateNodePosition(change.id, change.position);
+          }
         } else if (change.type === "remove") {
           removeNode(change.id);
         } else if (change.type === "select") {
           selectNode(change.selected ? change.id : null);
         }
       });
-      // applyNodeChanges 用于内部状态同步，但我们用 zustand 管理，这里不需要
-      void applyNodeChanges;
     },
     [updateNodePosition, removeNode, selectNode],
   );
@@ -100,7 +87,15 @@ export function NodeEditor({ textbookId, chapterId, classes }: Props) {
   );
 
   return (
-    <div className="w-full h-full">
+    <div className="w-full h-full relative">
+      {doc.nodes.length === 0 && (
+        <div className="absolute inset-0 flex items-center justify-center pointer-events-none z-10">
+          <div className="text-center text-on-surface-variant">
+            <p className="text-lg font-medium">{t("editor.canvasEmpty")}</p>
+            <p className="text-sm mt-1">{t("editor.canvasEmptyHint")}</p>
+          </div>
+        </div>
+      )}
       <ReactFlow
         nodes={rfNodes}
         edges={rfEdges}
@@ -129,7 +124,8 @@ export function NodeEditor({ textbookId, chapterId, classes }: Props) {
         <MiniMap
           className="!bg-surface !border-outline-variant"
           nodeColor={(n) => {
-            const data = n.data as unknown as LessonPlanNode;
+            const nodeData = (n.data as { node?: LessonPlanNode }).node;
+            if (!nodeData) return "#9e9e9e";
             const colors: Record<string, string> = {
               objective: "#4caf50",
               key_point: "#f44336",
@@ -144,12 +140,10 @@ export function NodeEditor({ textbookId, chapterId, classes }: Props) {
               rich_text: "#9e9e9e",
               reflection: "#cddc39",
             };
-            return colors[data.type] ?? "#9e9e9e";
+            return colors[nodeData.type] ?? "#9e9e9e";
           }}
         />
       </ReactFlow>
-      {/* 隐藏的 props 传递，避免 unused 警告 */}
-      <span className="hidden" data-textbook={textbookId} data-chapter={chapterId} data-classes={classes?.length} />
     </div>
   );
 }