fix(products): extract lexical AST and JSON-LD data correctly from productTabs block

tests/lexical.test.ts

@@ -0,0 +1,27 @@
+import { describe, it, expect } from 'vitest';
+import { lexicalToMarkdown } from '../lib/mdx-utils';
+
+describe('lexicalToMarkdown', () => {
+  it('should convert lexical AST to markdown', () => {
+    const ast = {
+      type: 'root',
+      children: [
+        {
+          type: 'paragraph',
+          children: [
+            { type: 'text', text: 'Hello ' },
+            { type: 'text', text: 'World', format: 1 }, // bold
+          ],
+        },
+        {
+          type: 'heading',
+          tag: 'h2',
+          children: [{ type: 'text', text: 'Title' }],
+        },
+      ],
+    };
+
+    const result = lexicalToMarkdown(ast);
+    expect(result).toBe('Hello **World**\n\n## Title\n\n');
+  });
+});