feat(chat): 引入 @ant-design/x 组件 — Sender/Conversations/XMarkdown 替代手动拼装

- ConfigProvider → XProvider（ConsoleShell + test-utils）
- ChatSidebar → Conversations（menu dropdown + MoreOutlined trigger）
- ChatInputArea → Sender（footer 左右排版 + 模型 Select + 自动清空）
- Streamdown → XMarkdown（streaming hasNextChunk 映射 AI SDK 状态）
- CSS 清理 ~94 行废弃样式，新增统一布局规则
- 删除 streamdown 依赖

skills-lock.json

@@ -18,6 +18,20 @@
       "sourceType": "github",
       "skillPath": "skills/antd/SKILL.md",
       "computedHash": "5e26c8042060bb811118927b5daf637af7929a00fa973dd8f5f804f3ba6e2bf2"
+    },
+    "x-components": {
+      "source": "ant-design/x",
+      "ref": "main",
+      "sourceType": "github",
+      "skillPath": "packages/x-skill/skills/x-components/SKILL.md",
+      "computedHash": "ebc195a3a5020b6d4f4533adf2e0af33253919f0c704947e727f877aba23a4c2"
+    },
+    "x-markdown": {
+      "source": "ant-design/x",
+      "ref": "main",
+      "sourceType": "github",
+      "skillPath": "packages/x-skill/skills/x-markdown/SKILL.md",
+      "computedHash": "2d26b8eda1692929e99a8b6163ef8b206f1f096a4a84507b50dbe836a7ec041e"
     }
   }
 }