refactor: 移除多列布局功能及相关代码

apps/DocFlow/src/app/docs/_components/DocumentSidebar/BlocksTab.tsx

@@ -159,13 +159,6 @@ const BlocksTab = () => {
       blockType: 'chart',
       category: 'data',
     },
-    {
-      icon: 'LayoutDashboard',
-      label: '多列布局',
-      description: '创建多列内容布局',
-      blockType: 'columns',
-      category: 'layout',
-    },
     {
       icon: 'Minus',
       label: '分割线',

apps/DocFlow/src/extensions/Document/Document.ts

@@ -1,7 +1,7 @@
 import { Document as TiptapDocument } from '@tiptap/extension-document';
 
 export const Document = TiptapDocument.extend({
-  content: '(block|columns)+',
+  content: 'block+',
 });
 
 export default Document;

apps/DocFlow/src/extensions/DragHandler/DragHandler.ts

@@ -288,22 +288,6 @@ class ChartBlockStrategy implements BlockContentStrategy {
   }
 }
 
-// 增加多列块策略
-class ColumnsBlockStrategy implements BlockContentStrategy {
-  create() {
-    return {
-      type: 'columns',
-      attrs: {
-        rows: 2,
-      },
-      content: [
-        { type: 'column', content: [{ type: 'paragraph' }] },
-        { type: 'column', content: [{ type: 'paragraph' }] },
-      ],
-    };
-  }
-}
-
 // 增加倒计时组件策略
 class CountdownBlockStrategy implements BlockContentStrategy {
   create() {
@@ -345,7 +329,6 @@ class BlockContentStrategyFactory {
     ['divider', new HorizontalRulerBlockStrategy()],
     ['ai', new AIBlockStrategy()],
     ['chart', new ChartBlockStrategy()],
-    ['columns', new ColumnsBlockStrategy()],
     ['countdown', new CountdownBlockStrategy()],
   ]);