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/package.json

@@ -9,12 +9,19 @@
     "lint": "next lint"
   },
   "dependencies": {
+    "hast-util-to-jsx-runtime": "^2.3.6",
     "lucide-react": "^0.460.0",
     "next": "^16.0.0",
     "react": "^19.0.0",
     "react-dom": "^19.0.0",
     "react-easy-crop": "^6.2.3",
-    "react-markdown": "^9.0.1"
+    "react-markdown": "^9.0.1",
+    "rehype-pretty-code": "^0.14.5",
+    "remark-gfm": "^4.0.1",
+    "remark-parse": "^11.0.0",
+    "remark-rehype": "^11.1.2",
+    "shiki": "^4.4.3",
+    "unified": "^11.0.5"
   },
   "devDependencies": {
     "@tailwindcss/postcss": "^4.0.0",