ui: 抽离流式消息渲染组件并增强富文本显示；

将助手消息渲染从页面内联逻辑拆分为独立组件，接入 Markdown/GFM、代码高亮与公式渲染，提升流式输出在表格、代码块等主流格式下的展示能力。

Made-with: Cursor

package.json

@@ -28,9 +28,16 @@
     "@microsoft/fetch-event-source": "^2.0.1",
     "antd": "^6.3.5",
     "axios": "^1.15.0",
+    "highlight.js": "^11.11.1",
+    "katex": "^0.16.45",
     "react": "^19.2.4",
     "react-dom": "^19.2.4",
-    "react-router-dom": "^7.13.2"
+    "react-markdown": "^10.1.0",
+    "react-router-dom": "^7.13.2",
+    "rehype-highlight": "^7.0.2",
+    "rehype-katex": "^7.0.1",
+    "remark-gfm": "^4.0.1",
+    "remark-math": "^6.0.0"
   },
   "devDependencies": {
     "@eslint/js": "^10.0.1",