fix: 修复flake8 lint检查错误

- 删除废弃的 admin_positions_backup.py 备份文件
- 修复 courses.py 缺失的 select 导入
- 修复 coze_gateway.py 异常变量作用域问题
- 修复 scheduler_service.py 无用的 global 声明
- 添加 TYPE_CHECKING 导入解决模型前向引用警告

backend/app/models/growth_path.py

@@ -2,10 +2,14 @@
 成长路径相关数据库模型
 """
 from enum import Enum
-from typing import List, Optional
+from typing import List, Optional, TYPE_CHECKING
 from datetime import datetime
 from decimal import Decimal
 
+if TYPE_CHECKING:
+    from app.models.course import Course
+    from app.models.user import User
+
 from sqlalchemy import (
     String,
     Text,
@@ -84,7 +88,7 @@ class GrowthPathNode(BaseModel, SoftDeleteMixin):
     )
 
     # 关联关系
-    growth_path: Mapped["GrowthPath"] = relationship(
+    growth_path: Mapped["GrowthPath"] = relationship(  # noqa: F821
         "GrowthPath", back_populates="nodes"
     )
     course: Mapped["Course"] = relationship("Course")
@@ -146,7 +150,7 @@ class UserGrowthPathProgress(BaseModel):
 
     # 关联关系
     user: Mapped["User"] = relationship("User")
-    growth_path: Mapped["GrowthPath"] = relationship("GrowthPath")
+    growth_path: Mapped["GrowthPath"] = relationship("GrowthPath")  # noqa: F821
 
 
 class UserNodeCompletion(BaseModel):
@@ -203,4 +207,4 @@ class UserNodeCompletion(BaseModel):
     node: Mapped["GrowthPathNode"] = relationship(
         "GrowthPathNode", back_populates="user_completions"
     )
-    growth_path: Mapped["GrowthPath"] = relationship("GrowthPath")
+    growth_path: Mapped["GrowthPath"] = relationship("GrowthPath")  # noqa: F821