refactor(lesson-preparation): 主编辑器三栏布局（结构树 + 纸 + 详情面板）

- 移除 NodeEditor/NodeEditPanel 导入和 JSX
- 改为 StructureTree + PaperEditor + DetailPanel 三栏布局
- 新增 AnchorMigrationBanner
- 移除 aiContentGenerator prop（V4 DetailPanel 自带 AI 按钮）
- 删除 node-edit-panel.tsx（不再被引用）
- 删除 ai-content-generator-slot.tsx（依赖 node-edit-panel）

src/app/(dashboard)/teacher/lesson-plans/[planId]/edit/page.tsx

@@ -11,8 +11,6 @@ import { Permissions } from "@/shared/types/permissions"
 import { Skeleton } from "@/shared/components/ui/skeleton"
 import { AiClientProvider } from "@/modules/ai/context/ai-client-provider"
 import { createCoreAiClientService } from "@/modules/ai/context/create-ai-client-service"
-// P0-11 修复：通过 slot 组件注入 AI 功能，避免备课模块直接 import @/modules/ai
-import { AiContentGeneratorSlot } from "./ai-content-generator-slot"
 
 export const dynamic = "force-dynamic"
 
@@ -70,7 +68,6 @@ export default async function EditLessonPlanPage({
               textbookTitle={textbookTitle}
               chapterTitle={chapterTitle}
               classes={classes}
-              aiContentGenerator={AiContentGeneratorSlot}
             />
           </Suspense>
         </div>