fix: 统一所有服务时间为北京时间 + 处理/忽略时计算告警时长

- notify_dispatch: _mark_false_alarm 使用 beijing_now() + 计算 duration_ms
- alarm_event_service: handle_alarm 处理时自动计算 duration_ms 和 last_frame_time
- notification_service: datetime.utcnow() 替换为 beijing_now()
- device_service: datetime.now(timezone.utc) 替换为 beijing_now()

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

app/services/notification_service.py

@@ -9,6 +9,7 @@ from typing import Dict, Any, List, Set
 from fastapi import WebSocket
 
 from app.utils.logger import logger
+from app.utils.timezone import beijing_now
 
 
 class ConnectionManager:
@@ -80,7 +81,7 @@ class NotificationService:
         message = {
             "event": "new_alert",
             "data": alert_data,
-            "timestamp": datetime.utcnow().isoformat(),
+            "timestamp": beijing_now().isoformat(),
         }
         await self._manager.broadcast(message)
         logger.debug(f"已广播新告警通知: {alert_data.get('alert_no', 'N/A')}")
@@ -90,7 +91,7 @@ class NotificationService:
         message = {
             "event": "alert_updated",
             "data": alert_data,
-            "timestamp": datetime.utcnow().isoformat(),
+            "timestamp": beijing_now().isoformat(),
         }
         await self._manager.broadcast(message)
 
@@ -99,7 +100,7 @@ class NotificationService:
         message = {
             "event": "device_status",
             "data": device_data,
-            "timestamp": datetime.utcnow().isoformat(),
+            "timestamp": beijing_now().isoformat(),
         }
         await self._manager.broadcast(message)
 
@@ -108,7 +109,7 @@ class NotificationService:
         message = {
             "event": f"work_order_{event_type}",
             "data": order_data,
-            "timestamp": datetime.utcnow().isoformat(),
+            "timestamp": beijing_now().isoformat(),
         }
         await self._manager.broadcast(message)
 
@@ -121,7 +122,7 @@ class NotificationService:
         message = {
             "event": event,
             "data": data,
-            "timestamp": datetime.utcnow().isoformat(),
+            "timestamp": beijing_now().isoformat(),
         }
 
         async def _broadcast():