feat: 统一聊天助手头像

- 工作流运行状态、智能体正式聊天与试运行展示助手头像

- 新增默认机器人头像及消息、空状态回退组件

easyflow-ui-admin/app/src/views/ai/agent-chat/index.vue

@@ -24,6 +24,7 @@ import {
   ChatImageAttachments,
   ChatTimeline,
   ChatTimelineBuilder,
+  defaultAssistantAvatar,
 } from '@easyflow/common-ui';
 import { copyTextToClipboard } from '@easyflow/utils';
 
@@ -1240,6 +1241,7 @@ onBeforeUnmount(() => {
         />
         <ChatTimeline
           v-else
+          :assistant-avatar="selectedAgent?.avatar || defaultAssistantAvatar"
           :items="timelineItems"
           :document-loader="loadAgentChatDocument"
           :image-loader="loadAgentChatImage"