修复数据库模型外键约束和代码质量问题

- 为User.created_by添加ForeignKey约束，确保数据完整性
- 修复AdjustmentEnum枚举命名（yes/no -> YES/NO）
- 统一User模型的relationship配置，使用back_populates替代backref
- 移除User.created_projects的级联删除配置，保持与Project模型一致

backend/src/models/project.py

@@ -6,8 +6,8 @@ from ..config.database import Base
 
 
 class AdjustmentEnum(str, Enum):
-    yes = "是"
-    no = "否"
+    YES = "是"
+    NO = "否"
 
 
 class Project(Base):
@@ -48,7 +48,7 @@ class Project(Base):
 
     # 成本控制
     total_cost_control = Column(Numeric(15, 2), comment="总体成本（控制）")
-    is_adjusted = Column(Enum(AdjustmentEnum), default=AdjustmentEnum.no, index=True, comment="是否调整")
+    is_adjusted = Column(Enum(AdjustmentEnum), default=AdjustmentEnum.NO, index=True, comment="是否调整")
     labor_cost_control = Column(Numeric(15, 2), comment="人工成本（控制）")
     labor_cost_planned = Column(Numeric(15, 2), comment="农民工工资（计划）")
     labor_cost_paid = Column(Numeric(15, 2), comment="农民工工资（实付）")

backend/src/models/user.py

@@ -1,5 +1,5 @@
 # backend/src/models/user.py
-from sqlalchemy import Column, Integer, String, Boolean, DateTime, Enum
+from sqlalchemy import Column, Integer, String, Boolean, DateTime, Enum, ForeignKey
 from sqlalchemy.sql import func
 from sqlalchemy.orm import relationship
 from ..config.database import Base
@@ -23,7 +23,7 @@ class User(Base):
     email = Column(String(100), unique=True, index=True, comment="邮箱")
     phone = Column(String(20), comment="电话")
     is_active = Column(Boolean, default=True, index=True, comment="是否激活")
-    created_by = Column(Integer, comment="创建人ID")
+    created_by = Column(Integer, ForeignKey("users.id", ondelete="RESTRICT"), comment="创建人ID")
     created_at = Column(
         DateTime,
         server_default=func.now(),
@@ -36,5 +36,6 @@ class User(Base):
         comment="更新时间",
     )
 
-    creator = relationship("User", remote_side="User.id", backref="created_users")
-    created_projects = relationship("Project", back_populates="creator", cascade="all, delete-orphan")
+    created_users = relationship("User", back_populates="creator")
+    creator = relationship("User", remote_side="User.id", back_populates="created_users")
+    created_projects = relationship("Project", back_populates="creator")