refactor(backend): adopt typed SQLAlchemy models

apps/backend/models/check_in_task.py

@@ -1,45 +1,57 @@
-from sqlalchemy import Column, Integer, String, Boolean, Text, DateTime, ForeignKey, Index
-from sqlalchemy.orm import relationship
+from datetime import datetime
+from typing import TYPE_CHECKING
+
+from sqlalchemy import Boolean, DateTime, ForeignKey, Index, String, Text
+from sqlalchemy.orm import Mapped, mapped_column, relationship
 from sqlalchemy.sql import func
+
 from backend.models.database import Base
 
+if TYPE_CHECKING:
+    from backend.models.check_in_record import CheckInRecord
+    from backend.models.user import User
+
 
 class CheckInTask(Base):
     """打卡任务模型"""
 
     __tablename__ = "check_in_tasks"
 
-    id = Column(Integer, primary_key=True, index=True, autoincrement=True)
-    user_id = Column(
-        Integer,
+    id: Mapped[int] = mapped_column(primary_key=True, index=True, autoincrement=True)
+    user_id: Mapped[int] = mapped_column(
         ForeignKey("users.id", ondelete="CASCADE"),
-        nullable=False,
         index=True,
         comment="用户 ID",
     )
-    payload_config = Column(
+    payload_config: Mapped[str] = mapped_column(
         Text,
         default="{}",
         nullable=False,
         comment="完整的 payload 配置 JSON（从模板生成，包含 ThreadId 和所有字段）",
     )
-    name = Column(String(100), default="", comment="任务名称（用户自定义）")
-    is_active = Column(Boolean, default=True, comment="是否启用自动打卡（不影响手动打卡）")
-    cron_expression = Column(
+    name: Mapped[str] = mapped_column(String(100), default="", comment="任务名称（用户自定义）")
+    is_active: Mapped[bool] = mapped_column(
+        Boolean, default=True, comment="是否启用自动打卡（不影响手动打卡）"
+    )
+    cron_expression: Mapped[str | None] = mapped_column(
         String(100),
         default="0 20 * * *",
         nullable=True,
         comment="Crontab 表达式（NULL 表示禁用自动打卡，否则按表达式执行）",
     )
-    created_at = Column(DateTime(timezone=True), server_default=func.now(), comment="创建时间")
-    updated_at = Column(DateTime(timezone=True), onupdate=func.now(), comment="更新时间")
+    created_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), server_default=func.now(), comment="创建时间"
+    )
+    updated_at: Mapped[datetime | None] = mapped_column(
+        DateTime(timezone=True), onupdate=func.now(), comment="更新时间"
+    )
 
     # 关联用户
-    user = relationship("User", back_populates="tasks")
+    user: Mapped["User"] = relationship(back_populates="tasks")
 
     # 关联打卡记录
-    check_in_records = relationship(
-        "CheckInRecord", back_populates="task", cascade="all, delete-orphan"
+    check_in_records: Mapped[list["CheckInRecord"]] = relationship(
+        back_populates="task", cascade="all, delete-orphan"
     )
 
     # 添加索引：加速查询