perf: WebSocket只在状态变化时广播，减少无效消息

server.js

@@ -136,11 +136,10 @@ function startCarouselTimer() {
         const startTime = parseInt(getConfig('current_group_start_time') || '0');
         const currentGroup = groups[idx];
 
-        if (currentGroup.display_seconds === 0) {
-            broadcastState();
-            return;
-        }
+        // 无限时分组，不需要切换
+        if (currentGroup.display_seconds === 0) return;
 
+        // 首次启动，记录开始时间并广播
         if (startTime === 0) {
             setConfig('current_group_start_time', Math.floor(Date.now() / 1000));
             broadcastState();
@@ -150,12 +149,13 @@ function startCarouselTimer() {
         const now = Math.floor(Date.now() / 1000);
         const elapsed = now - startTime;
 
+        // 时间到了，切换分组并广播
         if (elapsed >= currentGroup.display_seconds) {
             const nextIdx = findNextGroupIndex(groups, idx);
             setConfig('current_group_index', nextIdx);
             setConfig('current_group_start_time', Math.floor(Date.now() / 1000));
-        }
             broadcastState();
+        }
     }, 1000);
 }