fix: 重命名通知渠道模型避免与 alert 模块冲突

- NotificationChannel -> TaskNotifyChannel
- platform_notification_channels -> platform_task_notify_channels

backend/app/models/notification_channel.py

@@ -1,12 +1,12 @@
-"""通知渠道模型"""
+"""任务通知渠道模型"""
 from datetime import datetime
 from sqlalchemy import Column, Integer, String, Enum, Boolean, DateTime
 from ..database import Base
 
 
-class NotificationChannel(Base):
-    """通知渠道表"""
-    __tablename__ = "platform_notification_channels"
+class TaskNotifyChannel(Base):
+    """任务通知渠道表（用于定时任务推送）"""
+    __tablename__ = "platform_task_notify_channels"
     
     id = Column(Integer, primary_key=True, autoincrement=True)
     tenant_id = Column(String(50), nullable=False)