fix(server): 完善列车接近音频的处理与日志记录

新增列车接近音频入队和构建失败的日志输出
调整音频任务优先级为1，中断模式改为ifLower
修复音频构建为空时的静默失败问题

CloudServer/server.js

@@ -2027,18 +2027,21 @@ function handleTrainApproaching(ws, data) {
     const audioId = `approaching-${stationCode}-${Date.now()}`;
     const built = buildSequenceWavFile(seq);
     if (built) {
+        log('INFO', `Pre-arrival audio queued for ${stationName}: ${audioId} (${built.durationSec.toFixed(2)}s)`);
         enqueueStationAudioTask(stationName, ws, {
             audioFormat: built.audioFormat,
             sourcePath: built.sourcePath,
             streamUrl: built.streamUrl,
             durationSec: built.durationSec,
-            priority: 0,
-            interruptMode: 'none',
+            priority: 1,
+            interruptMode: 'ifLower',
             source: 'train_approaching',
             audioId,
             consoleStreamStart: { type: 'stream_start', station: stationName, seq, streamName: getStationStreamName(stationName), hlsUrl: getStationHlsUrl(getStationStreamName(stationName)) },
             consoleStreamEnd: { type: 'stream_end', station: stationName }
         });
+    } else {
+        log('WARN', `Pre-arrival audio build returned empty for ${stationName}: ${audioId}`);
     }
 }