feat(approval): 审批单/节点状态机与二次分配接入（开关自动通过）

- approval_orders/approval_steps 服务层：submit_order（不 commit 不嵌套
  audit，业务写路径统一收口）+ act 节点动作 + 分页/详情
- 开关关闭=提单即两级「自动通过」留痕（action=3，operator 记系统）；
  开启=财务→领导流转，一驳全驳，驳回必填意见
- 节点准入严格按角色（status=1 仅财务、status=2 仅领导），admin 不代办；
  模块准入 require_roles 依赖工厂（admin/finance/leader，营销后勤待
  澄清 #6 后放开）
- 业务接入：创建/编辑带方案即提单（空方案不提单）；再编辑自动撤回旧
  在途单（node=0/action=4 留痕）；AP 编号冲突 create 内可重取（外层
  重试兜底）、update 直接抛出防静默丢失
- conftest 兜底清理增审批单（AP 前缀）与开关参数种子基线恢复
- 集成 11 例：自动通过/两节点流转/驳回留痕/缺意见 400/节点准入 403/
  admin 不代办/重复操作 400/撤旧建新/模块准入

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

backend/app/api/router.py

@@ -15,6 +15,7 @@ from app.api.v1.business import businesses as business_businesses
 from app.api.v1.business import ratings as business_ratings
 from app.api.v1.business import receipts as business_receipts
 from app.api.v1.business import shipments as business_shipments
+from app.api.v1.system import approvals as system_approvals
 from app.api.v1.system import business_roles as system_business_roles
 from app.api.v1.system import logs as system_logs
 from app.api.v1.system import params as system_params
@@ -38,6 +39,7 @@ system_router.include_router(system_roles.router)
 system_router.include_router(system_business_roles.router)
 system_router.include_router(system_params.router)
 system_router.include_router(system_settings.router)
+system_router.include_router(system_approvals.router)
 system_router.include_router(system_logs.operation_router)
 system_router.include_router(system_logs.login_router)
 v1_router.include_router(system_router)