fix(消息列表): 调整滚动加载阈值从100降至20

优化消息列表滚动加载体验，降低触发加载更多的阈值，使用户在滚动到更接近底部时即可触发加载

@@ -38,7 +38,7 @@
 
 
         <!-- 消息列表内容 -->
         <!-- 消息列表内容 -->
         <scroll-view ref="scrollViewRef" class="conversation-list" :style="scrollStyle" :scroll-y="true"
         <scroll-view ref="scrollViewRef" class="conversation-list" :style="scrollStyle" :scroll-y="true"
-            @scrolltolower="loadMore" @scroll="scroll" :lower-threshold="100" :enable-flex="false"
+            @scrolltolower="loadMore" @scroll="scroll" :lower-threshold="20" :enable-flex="false"
             :scroll-top="scrollTop">
             :scroll-top="scrollTop">
             <view v-for="conversation in filteredConversations" :key="conversation.id"
             <view v-for="conversation in filteredConversations" :key="conversation.id"
                 class="conversation-item mt-2 mb-4 border-b border-gray-100 pb-2"
                 class="conversation-item mt-2 mb-4 border-b border-gray-100 pb-2"
@@ -209,7 +209,7 @@ const startPolling = () => {
     if (pollingTimer.value) {
     if (pollingTimer.value) {
         clearInterval(pollingTimer.value)
         clearInterval(pollingTimer.value)
     }
     }
-    
+
     // 启动新的定时器
     // 启动新的定时器
     pollingTimer.value = setInterval(() => {
     pollingTimer.value = setInterval(() => {
         pollMessages()
         pollMessages()