优化登录任务界面 + 修复时间显示 + 增加删除功能

- 筛选栏改为单行横排，概览精简为一行文字
- 任务列表全宽展示，日志移到底部可折叠
- 页面使用百分比布局，一屏展示无外层滚动
- 登录任务增加单条删除和批量删除功能
- 后端: datetime.utcnow 替换为 datetime.now(timezone.utc)
- 后端: schemas 序列化统一输出带时区 ISO 格式
- 前端: 新增 utils/time.ts 统一时间格式化工具
- 前端: CookiePage/LoginTasksPage 时间列使用 formatTime()

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

web/backend/models.py

@@ -1,6 +1,6 @@
 """ORM 模型"""
 
-from datetime import datetime
+from datetime import datetime, timezone
 from sqlalchemy import (
     Column, Integer, String, Boolean, Text, DateTime, ForeignKey, JSON,
 )
@@ -8,6 +8,11 @@ from sqlalchemy.orm import relationship
 from .database import Base
 
 
+def _utcnow():
+    """返回时区感知的 UTC 当前时间，替代 _utcnow()。"""
+    return datetime.now(timezone.utc)
+
+
 class User(Base):
     """系统用户"""
     __tablename__ = "users"
@@ -19,8 +24,8 @@ class User(Base):
     is_active = Column(Boolean, default=True)
     remark = Column(String(256), default="")
     custom_permissions = Column(JSON, nullable=True, comment="自定义权限列表，null表示使用角色默认权限")
-    created_at = Column(DateTime, default=datetime.utcnow)
-    updated_at = Column(DateTime, default=datetime.utcnow, onupdate=datetime.utcnow)
+    created_at = Column(DateTime, default=_utcnow)
+    updated_at = Column(DateTime, default=_utcnow, onupdate=_utcnow)
 
     # 客服被分配的账号
     assigned_accounts = relationship("Account", back_populates="assigned_user", foreign_keys="Account.assigned_to")
@@ -40,7 +45,7 @@ class Account(Base):
     assigned_to = Column(Integer, ForeignKey("users.id"), nullable=True, index=True)
     tag = Column(String(64), default="")
     remark = Column(String(256), default="")
-    created_at = Column(DateTime, default=datetime.utcnow)
+    created_at = Column(DateTime, default=_utcnow)
 
     assigned_user = relationship("User", back_populates="assigned_accounts", foreign_keys=[assigned_to])
     login_tasks = relationship("LoginTask", back_populates="account")
@@ -57,7 +62,7 @@ class LoginTask(Base):
     cookie = Column(Text, default="")
     message = Column(String(512), default="")
     created_by = Column(Integer, ForeignKey("users.id"), nullable=False)
-    created_at = Column(DateTime, default=datetime.utcnow)
+    created_at = Column(DateTime, default=_utcnow)
     finished_at = Column(DateTime, nullable=True)
 
     account = relationship("Account", back_populates="login_tasks")
@@ -88,4 +93,4 @@ class AuditLog(Base):
     action = Column(String(128), nullable=False)
     target = Column(String(256), default="")
     detail = Column(Text, default="")
-    created_at = Column(DateTime, default=datetime.utcnow)
+    created_at = Column(DateTime, default=_utcnow)