feat(migration): V6 系统设置/二次分配/审批表与角色参数种子

- 新增 system_settings（公司信息单行）/ business_secondary_allocations（二次
  分配明细，比例不强制合计满额，分摊计算待澄清另批）/ approval_orders+
  approval_steps（三级审批状态机，开关关闭自动通过留痕）
- roles 种子新增营销后勤/财务/领导三职能角色；内置保护改 BUILTIN_ROLE_CODES
  白名单（roles 表无 is_builtin 列，不加列）
- PARAM_REGISTRY 首例 BOOL：两个审批开关（16→18 项，种子双写）
- 双轨同步：V6 导出 SQL + init-dev.sql（表/索引/种子/版本号 79bcc5aa98d4）
- 测试同步：EXPECTED_TABLES 四新表、角色种子断言 5 角色、目录断言 18 项
  八分组、BOOL 校验边界；迁移 downgrade 修 1553（只保留 drop_table）并补
  行级种子反向清理

Co-Authored-By: Claude Code <noreply@anthropic.com>

backend/app/models/__init__.py

@@ -9,8 +9,9 @@
 `Base.metadata` 包含全部表，漏掉一张就会生成「删除该表」的迁移。
 """
 
+from app.models.approval import ApprovalOrder, ApprovalStep
 from app.models.base import Base, TimestampMixin
-from app.models.business import Business, BusinessItem, BusinessStatusLog
+from app.models.business import Business, BusinessItem, BusinessStatusLog, SecondaryAllocation
 from app.models.business_role import BusinessRole
 from app.models.customer import Customer, OwnershipChangeLog
 from app.models.login_log import LoginLog
@@ -22,9 +23,12 @@ from app.models.rating import CustomerRatingGrade
 from app.models.receipt import Receipt
 from app.models.role import Permission, Role, RolePermission
 from app.models.shipment import Shipment, ShipmentItem
+from app.models.system_setting import SystemSetting
 from app.models.user import User, UserRole
 
 __all__ = [
+    "ApprovalOrder",
+    "ApprovalStep",
     "Base",
     "Business",
     "BusinessItem",
@@ -46,8 +50,10 @@ __all__ = [
     "Receipt",
     "Role",
     "RolePermission",
+    "SecondaryAllocation",
     "Shipment",
     "ShipmentItem",
+    "SystemSetting",
     "TimestampMixin",
     "User",
     "UserRole",