feat：样式美化

frontend/src/components/ChatPanel/index.tsx

@@ -44,13 +44,17 @@ export function ChatPanel({ messages, currentReply, connectionStatus }: ChatPane
     if (connectionStatus !== "connected") {
       return (
         <div className="chat-panel chat-panel--empty">
+          <span className="chat-panel--empty-icon">💬</span>
           <p>点击下方按钮开始对话</p>
+          <span className="chat-panel--empty-hint">连接后可通过摄像头和麦克风与 AI 交互</span>
         </div>
       );
     }
     return (
       <div className="chat-panel chat-panel--empty">
+        <span className="chat-panel--empty-icon">🎙️</span>
         <p>对着摄像头说话即可</p>
+        <span className="chat-panel--empty-hint">AI 会自动识别你的语音并分析画面</span>
       </div>
     );
   }