feat(web): 优化聊天页面语音控制图标和空状态图片

- 将文本转语音的播放和停止图标替换为 Ant Design 图标
- 将空状态图片从 PNG 改为 SVG 格式，优化视觉效果

web/components/chat/chat-content/agent-messages.tsx

@@ -1,5 +1,9 @@
 import useTextToSpeech from '@/hooks/useTextToSpeech';
 import { Button } from 'antd';
+import {
+  SoundOutlined,
+  MutedOutlined,
+} from '@ant-design/icons';
 import { useMemo } from 'react';
 import ReferencesContent from './ReferencesContent';
 import styles from './common.module.scss';
@@ -81,11 +85,11 @@ function AgentMessages({ data }: Props) {
           <div className={`space-x-2 ${item.receiver === '?' ? 'hidden' : ''}`}>
             {!isSpeaking ? (
               <Button size='small' onClick={handleSpeak}>
-                📢
+                <SoundOutlined />
               </Button>
             ) : (
               <Button size='small' danger onClick={() => stop(textId)}>
-                🛑
+                <MutedOutlined />
               </Button>
             )}
           </div>

web/components/common/MyEmpty.tsx

@@ -14,7 +14,7 @@ function MyEmpty({ className, error, description, refresh }: Props) {
 
   return (
     <Empty
-      image='/empty.png'
+      image='/empty.svg'
       imageStyle={{ width: 320, height: 196, margin: '0 auto', maxWidth: '100%', maxHeight: '100%' }}
       className={classNames('flex items-center justify-center flex-col h-full w-full', className)}
       description={