refactor(backend): adopt typed SQLAlchemy models

apps/backend/models/task_template.py

@@ -1,6 +1,11 @@
-from sqlalchemy import Column, Integer, String, Boolean, Text, DateTime, ForeignKey
-from sqlalchemy.orm import relationship
+from __future__ import annotations
+
+from datetime import datetime
+
+from sqlalchemy import Boolean, DateTime, ForeignKey, String, Text
+from sqlalchemy.orm import Mapped, mapped_column, relationship
 from sqlalchemy.sql import func
+
 from backend.models.database import Base
 
 
@@ -9,27 +14,33 @@ class TaskTemplate(Base):
 
     __tablename__ = "task_templates"
 
-    id = Column(Integer, primary_key=True, index=True, autoincrement=True)
-    name = Column(String(100), nullable=False, comment="模板名称")
-    description = Column(Text, nullable=True, comment="模板描述")
+    id: Mapped[int] = mapped_column(primary_key=True, index=True, autoincrement=True)
+    name: Mapped[str] = mapped_column(String(100), nullable=False, comment="模板名称")
+    description: Mapped[str | None] = mapped_column(Text, nullable=True, comment="模板描述")
 
     # 父模板 ID（用于继承）
-    parent_id = Column(
-        Integer,
+    parent_id: Mapped[int | None] = mapped_column(
         ForeignKey("task_templates.id", ondelete="SET NULL"),
         nullable=True,
         comment="父模板 ID",
     )
 
     # 字段配置（JSON 格式）
-    field_config = Column(Text, nullable=False, comment="字段配置（JSON）")
+    field_config: Mapped[str] = mapped_column(Text, nullable=False, comment="字段配置（JSON）")
 
-    is_active = Column(Boolean, default=True, comment="是否启用")
-    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")
+    is_active: Mapped[bool] = mapped_column(Boolean, default=True, comment="是否启用")
+    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"
+    )
 
     # 自引用关系：父模板和子模板
-    parent = relationship("TaskTemplate", remote_side=[id], backref="children")
+    parent: Mapped[TaskTemplate | None] = relationship(
+        remote_side="TaskTemplate.id", back_populates="children"
+    )
+    children: Mapped[list[TaskTemplate]] = relationship(back_populates="parent")
 
     def __repr__(self):
         return f"<TaskTemplate(id={self.id}, name='{self.name}', is_active={self.is_active})>"