feat: enforce required department and role codes with validation

- Updated DeptModel and RoleModel to make the `code` field mandatory and unique.
- Enhanced DeptCreateSchema and RoleCreateSchema to require a valid `code` format, ensuring it starts with a letter and is 2-16 characters long.
- Implemented validation logic in the backend to check for existing codes during updates, preventing duplicates.
- Adjusted frontend forms to reflect the required `code` field and added validation messages for user guidance.

backend/app/api/v1/module_system/role/model.py

@@ -74,8 +74,8 @@ class RoleModel(ModelMixin):
     __permission_strategy__: PermissionFilterStrategy = PermissionFilterStrategy.USER_ROLE
 
     name: Mapped[str] = mapped_column(String(64), nullable=False, comment="角色名称")
-    code: Mapped[str | None] = mapped_column(
-        String(16), nullable=True, index=True, comment="角色编码"
+    code: Mapped[str] = mapped_column(
+        String(16), nullable=False, unique=True, comment="角色编码"
     )
     order: Mapped[int] = mapped_column(Integer, nullable=False, default=999, comment="显示排序")
     data_scope: Mapped[int] = mapped_column(