refactor: 合并 biz_support_unit/biz_execution_unit/biz_service_org 为 biz_org, 删除 2 张孤儿表, 改 biz_person.work_unit → org_id FK

主要改动:
- SQL: biz_support_unit → biz_org, 加 org_type, 加 business_nature; 删 biz_execution_unit, biz_service_org
- SQL: biz_project.support_unit_id/name + service_org_id/name → org_id/name/type
- SQL: biz_meeting.support_unit_name → org_name
- SQL: biz_person.work_unit → org_id (FK)
- 后端: 新 BizOrg entity/mapper/service/controller
- 后端: BizProject/BizMeeting 字段重命名
- 后端: 删 12 个 BizSupportUnit/BizExecutionUnit/BizServiceOrg Java 文件
- 后端: BizPersonImportVO.workUnit → orgName (导入时查 biz_org 取 org_id)
- 后端: BizAuthController.registerExecutor 完整实现 (原 registerSupplier stub)
- 前端: 新 admin/Orgs.vue + manager/Orgs.vue (原 SupportUnits)
- 前端: RegisterExecutor.vue (原 RegisterSupplier, 单页 2 步)
- 前端: sponsor/executor/manager 多个文件 workUnit → orgId/orgName 重命名
- 前端: 统一 supplier → executor, 业务命名 sponsor(赞助方) / executor(执行方=供应商)
- 前端: 全工程 execution → executor (company type / role / person unit_type)

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