feat(system): 业务岗位角色管理接口与保护规则

- 四层实现：仓储（FOR UPDATE 锁行 + 引用计数钩子预留）/ schemas / service / api 共 7 个端点
- 保护规则：内置岗位禁删禁停、编码创建后不可改、模板须在注册表内（未注册 400）
- 写操作全走审计上下文；冒烟验证 7 项（含成功/失败双路径落日志）
- 端点：列表/新增/详情/编辑/删除/启停 + meta/templates 模板下拉

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

backend/app/api/router.py

@@ -8,6 +8,7 @@ from fastapi import APIRouter
 
 from app.api import health
 from app.api.v1 import auth
+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 roles as system_roles
 from app.api.v1.system import users as system_users
@@ -25,6 +26,7 @@ v1_router.include_router(auth.router)
 system_router = APIRouter(prefix="/system")
 system_router.include_router(system_users.router)
 system_router.include_router(system_roles.router)
+system_router.include_router(system_business_roles.router)
 system_router.include_router(system_logs.operation_router)
 system_router.include_router(system_logs.login_router)
 v1_router.include_router(system_router)