chore：时间居中

pages_tool/ai-chat/ai-chat-message.vue

@@ -59,7 +59,7 @@
           <view class="message-content">
             <!-- AI昵称固定，不可修改 - 左移到气泡上方 -->
             <view class="message-nickname ai-nickname">
-              <text>智能助手</text>
+              <text class="ai-nickname-text">智能助手</text>
               <text class="message-time">{{ formatTime(message.timestamp) }}</text>
             </view>
             <view class="message-bubble">
@@ -2172,6 +2172,7 @@ $radius-lg: 36rpx;
           font-size: 24rpx;
           color: #999;
           line-height: 1;
+          top:-15rpx;
         }
       }
 
@@ -2190,9 +2191,23 @@ $radius-lg: 36rpx;
         padding-left: 0;
         align-self: flex-start;
         margin-bottom: 4rpx;
-        justify-content: flex-start;
+        justify-content: space-between;
         display: flex;
         align-items: baseline;
+        width: 100%;
+        position: relative;
+        
+        .ai-nickname-text {
+          position: relative;
+          z-index: 1;
+        }
+        
+        .message-time {
+          position: absolute;
+          left: 50%;
+          transform: translateX(-50%);
+          margin-top: -2rpx;
+        }
       }
 
       /* 用户消息特有样式 */