fix: 统一数据库时间为北京时间（UTC+8）

- 新增 app/utils/timezone.py 提供 beijing_now() 工具函数
- models.py 所有表的 created_at/updated_at 默认值从 UTC 改为北京时间
- 解决 event_time（边缘端北京时间）与 handled_at（服务端UTC）差8小时的问题

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

app/models.py

@@ -4,6 +4,8 @@
 import enum
 import os
 from datetime import datetime, timezone
+
+from app.utils.timezone import beijing_now
 from typing import Optional
 from sqlalchemy import (
     Column, String, Integer, SmallInteger, BigInteger, Boolean, Float, DateTime, Text, Enum, JSON,
@@ -102,9 +104,9 @@ class Alert(Base):
     work_order_id = Column(Integer, ForeignKey("work_orders.id"), nullable=True)
 
     # 时间戳
-    created_at = Column(DateTime, default=lambda: datetime.now(timezone.utc))
-    updated_at = Column(DateTime, default=lambda: datetime.now(timezone.utc),
-                        onupdate=lambda: datetime.now(timezone.utc))
+    created_at = Column(DateTime, default=lambda: beijing_now())
+    updated_at = Column(DateTime, default=lambda: beijing_now(),
+                        onupdate=lambda: beijing_now())
 
     # 关系
     work_order = relationship("WorkOrder", back_populates="alerts", foreign_keys=[work_order_id])
@@ -175,9 +177,9 @@ class WorkOrder(Base):
     assigned_at = Column(DateTime, nullable=True)
     started_at = Column(DateTime, nullable=True)
     completed_at = Column(DateTime, nullable=True)
-    created_at = Column(DateTime, default=lambda: datetime.now(timezone.utc))
-    updated_at = Column(DateTime, default=lambda: datetime.now(timezone.utc),
-                        onupdate=lambda: datetime.now(timezone.utc))
+    created_at = Column(DateTime, default=lambda: beijing_now())
+    updated_at = Column(DateTime, default=lambda: beijing_now(),
+                        onupdate=lambda: beijing_now())
 
     # 关系
     alerts = relationship("Alert", back_populates="work_order", foreign_keys=[Alert.work_order_id])
@@ -231,9 +233,9 @@ class EdgeDevice(Base):
     # 扩展
     extra_info = Column(JSON, nullable=True)
 
-    created_at = Column(DateTime, default=lambda: datetime.now(timezone.utc))
-    updated_at = Column(DateTime, default=lambda: datetime.now(timezone.utc),
-                        onupdate=lambda: datetime.now(timezone.utc))
+    created_at = Column(DateTime, default=lambda: beijing_now())
+    updated_at = Column(DateTime, default=lambda: beijing_now(),
+                        onupdate=lambda: beijing_now())
 
     def to_dict(self) -> dict:
         return {
@@ -279,9 +281,9 @@ class AlarmEvent(Base):
     handler = Column(String(64), comment="处理人")
     handle_remark = Column(Text, comment="处理备注")
     handled_at = Column(DateTime, comment="处理时间")
-    created_at = Column(DateTime, default=lambda: datetime.now(timezone.utc))
-    updated_at = Column(DateTime, default=lambda: datetime.now(timezone.utc),
-                        onupdate=lambda: datetime.now(timezone.utc))
+    created_at = Column(DateTime, default=lambda: beijing_now())
+    updated_at = Column(DateTime, default=lambda: beijing_now(),
+                        onupdate=lambda: beijing_now())
 
     __table_args__ = (
         Index('idx_alarm_event_time', 'event_time'),
@@ -323,7 +325,7 @@ class AlarmEventExt(Base):
     ext_type = Column(String(32), comment="扩展类型: EDGE/POST/MANUAL")
     ext_data = Column(JSON, comment="扩展数据")
     roi_config = Column(JSON, comment="ROI配置快照")
-    created_at = Column(DateTime, default=lambda: datetime.now(timezone.utc))
+    created_at = Column(DateTime, default=lambda: beijing_now())
 
     def to_dict(self) -> dict:
         return {
@@ -349,7 +351,7 @@ class AlarmLlmAnalysis(Base):
     risk_score = Column(Integer, comment="风险评分 0-100")
     confidence_score = Column(Float, comment="分析置信度")
     suggestion = Column(Text, comment="处置建议")
-    created_at = Column(DateTime, default=lambda: datetime.now(timezone.utc))
+    created_at = Column(DateTime, default=lambda: beijing_now())
 
     def to_dict(self) -> dict:
         return {
@@ -413,8 +415,8 @@ class NotifyArea(Base):
     area_name = Column(String(100), nullable=False)
     description = Column(String(200), nullable=True)
     enabled = Column(SmallInteger, default=1)
-    created_at = Column(DateTime, default=datetime.now)
-    updated_at = Column(DateTime, default=datetime.now, onupdate=datetime.now)
+    created_at = Column(DateTime, default=beijing_now)
+    updated_at = Column(DateTime, default=beijing_now, onupdate=beijing_now)
 
 
 class CameraAreaBinding(Base):
@@ -424,7 +426,7 @@ class CameraAreaBinding(Base):
     id = Column(Integer, primary_key=True, autoincrement=True)
     camera_id = Column(String(64), unique=True, nullable=False, index=True)
     area_id = Column(String(36), nullable=False, index=True)
-    created_at = Column(DateTime, default=datetime.now)
+    created_at = Column(DateTime, default=beijing_now)
 
 
 class AreaPersonBinding(Base):
@@ -438,8 +440,8 @@ class AreaPersonBinding(Base):
     role = Column(String(20), default="SECURITY")
     notify_level = Column(Integer, default=1)
     enabled = Column(SmallInteger, default=1)
-    created_at = Column(DateTime, default=datetime.now)
-    updated_at = Column(DateTime, default=datetime.now, onupdate=datetime.now)
+    created_at = Column(DateTime, default=beijing_now)
+    updated_at = Column(DateTime, default=beijing_now, onupdate=beijing_now)
 
 
 # ==================== 数据库管理 ====================

app/utils/timezone.py

@@ -0,0 +1,20 @@
+"""
+时区工具
+
+本系统所有时间统一使用北京时间（UTC+8）。
+边缘端上报的 event_time 是北京时间，服务端生成的时间也使用北京时间，
+确保数据库中所有时间字段语义一致。
+"""
+
+from datetime import datetime, timezone, timedelta
+
+# 北京时区 UTC+8
+BEIJING_TZ = timezone(timedelta(hours=8))
+
+
+def beijing_now() -> datetime:
+    """返回当前北京时间（naive datetime，无时区信息）
+
+    用于数据库存储，与边缘端上报的 event_time 格式一致。
+    """
+    return datetime.now(BEIJING_TZ).replace(tzinfo=None)