refactor(generator): 优化代码生成模块接口和服务实现

- 修改接口定义，增加路径参数并完善请求描述，增强参数校验和依赖注入
- 优化CRUD层数据库操作，统一异步会话使用，删除多余db参数
- 增加业务表与字段模型关系级联删除配置，优化模型关联关系声明
- 精简pydantic模型，去除冗余校验装饰器，完善字段描述和必填约束
- 服务层增加类型检查和异常抛出，规范业务逻辑流程和错误提示
- 优化代码结构，调整模块导入顺序和注释，提升代码可读性和一致性

backend/app/api/v1/module_generator/gencode/model.py

@@ -2,7 +2,7 @@
 
 from typing import Optional, List
 from sqlalchemy import String, Integer, ForeignKey
-from sqlalchemy.orm import Mapped, mapped_column, relationship
+from sqlalchemy.orm import Mapped, mapped_column, relationship, declared_attr
 
 from app.core.base_model import CreatorMixin
 
@@ -30,7 +30,13 @@ class GenTableModel(CreatorMixin):
     gen_path: Mapped[Optional[str]] = mapped_column(String(200), nullable=True, default='/', comment='生成路径（不填默认项目路径）')
     options: Mapped[Optional[str]] = mapped_column(String(1000), nullable=True, comment='其它生成选项')
     
-    columns: Mapped[List['GenTableColumnModel']] = relationship('GenTableColumnModel', order_by='GenTableColumnModel.sort', back_populates='table')
+    # 关系定义
+    columns: Mapped[List['GenTableColumnModel']] = relationship(
+        'GenTableColumnModel', 
+        order_by='GenTableColumnModel.sort', 
+        back_populates='table',
+        cascade='all, delete-orphan'
+    )
 
 
 class GenTableColumnModel(CreatorMixin):
@@ -58,5 +64,16 @@ class GenTableColumnModel(CreatorMixin):
     dict_type: Mapped[Optional[str]] = mapped_column(String(200), nullable=True, default='', comment='字典类型')
     sort: Mapped[Optional[int]] = mapped_column(Integer, nullable=True, comment='排序')
 
-    table_id: Mapped[Optional[int]] = mapped_column(Integer, ForeignKey('gen_table.id'), nullable=True, comment='归属表编号')
-    table: Mapped['GenTableModel'] = relationship('GenTableModel', back_populates='columns')
+    # 外键关系
+    table_id: Mapped[Optional[int]] = mapped_column(
+        Integer, 
+        ForeignKey('gen_table.id', ondelete='CASCADE'), 
+        nullable=True, 
+        comment='归属表编号'
+    )
+    
+    # 关系定义
+    table: Mapped['GenTableModel'] = relationship(
+        'GenTableModel', 
+        back_populates='columns'
+    )