refactor: 移除多租户相关逻辑并清理冗余代码

本次提交完成以下主要变更：
1.  删除所有租户相关的初始化数据、配置和工具代码
2.  移除TicketModel的租户关联字段与校验逻辑
3.  重构菜单表名与关联外键，统一为sys_前缀
4.  为岗位、部门、工作流等模型添加唯一约束
5.  调整导入顺序与冗余代码，优化代码结构
6.  移除支付、PDF生成相关的依赖与工具类
7.  简化OpenAPI文档标签配置
8.  清理无效的枚举与冗余导入

backend/app/api/v1/module_task/workflow/flows/model.py

@@ -1,4 +1,4 @@
-from sqlalchemy import JSON, Integer, String, Text, UniqueConstraint
+from sqlalchemy import JSON, Integer, String, Text
 from sqlalchemy.orm import Mapped, mapped_column
 
 from app.core.base_model import ModelMixin, UserMixin
@@ -13,7 +13,7 @@ class WorkflowModel(ModelMixin, UserMixin):
     __loader_options__: list[str] = ["created_by", "updated_by", "deleted_by"]
 
     name: Mapped[str] = mapped_column(String(128), nullable=False, comment="流程名称")
-    code: Mapped[str] = mapped_column(String(64), nullable=False, comment="流程编码")
+    code: Mapped[str] = mapped_column(String(64), unique=True, nullable=False, comment="流程编码")
     nodes: Mapped[list | None] = mapped_column(JSON, nullable=True, comment="VueFlow节点")
     edges: Mapped[list | None] = mapped_column(JSON, nullable=True, comment="VueFlow连接线")
     status: Mapped[int] = mapped_column(Integer, default=0, nullable=False, comment="状态(0:草稿 1:已发布 2:已归档)", index=True)