feat(frontend): Markdown 支持 GFM、代码高亮与图片灯箱

统一 SSR/客户端渲染路径，评论与预览共用增强组件。

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/components/MarkdownEditor.tsx

@@ -17,7 +17,7 @@ import {
 } from "lucide-react";
 import { apiUploadPostImage } from "@/lib/api";
 import { toast } from "@/lib/toast";
-import MarkdownBody from "@/components/MarkdownBody";
+import MarkdownBodyClient from "@/components/MarkdownBodyClient";
 
 type MarkdownEditorProps = {
   value: string;
@@ -304,7 +304,7 @@ export default function MarkdownEditor({
       ) : (
         <div className="j13-md-preview">
           {value.trim() ? (
-            <MarkdownBody content={value} />
+            <MarkdownBodyClient content={value} />
           ) : (
             <p className="meta text-center py-16">暂无内容可预览</p>
           )}