fix: 告警上传COS路径日期改为北京时间

alarm_upload_worker.py 中 COS object key 的日期和死信时间戳
从 UTC 改为北京时间（UTC+8），与服务端和日志时间一致。

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

core/alarm_upload_worker.py

@@ -17,7 +17,9 @@ import json
 import logging
 import threading
 import time
-from datetime import datetime, timezone
+from datetime import datetime, timezone, timedelta
+
+_BEIJING_TZ = timezone(timedelta(hours=8))
 from typing import Any, Dict, Optional
 
 import redis
@@ -294,7 +296,7 @@ class AlarmUploadWorker:
                 return None
 
         # 生成 Object Key: alarms/{device_id}/{yyyy-MM-dd}/{alarm_id}.jpg
-        date_str = datetime.now(timezone.utc).strftime("%Y-%m-%d")
+        date_str = datetime.now(_BEIJING_TZ).strftime("%Y-%m-%d")
         object_key = f"alarms/{device_id}/{date_str}/{alarm_id}.jpg"
 
         try:
@@ -392,7 +394,7 @@ class AlarmUploadWorker:
         if retry_count > max_retry:
             # 超过最大重试次数，写入死信队列
             alarm_data["_dead_reason"] = error
-            alarm_data["_dead_at"] = datetime.now(timezone.utc).isoformat()
+            alarm_data["_dead_at"] = datetime.now(_BEIJING_TZ).isoformat()
             dead_json = json.dumps(alarm_data, ensure_ascii=False)
             self._redis.lpush(REDIS_KEY_ALARM_DEAD, dead_json)
             self._stats["dead_lettered"] += 1