refactor(server): 用已装库替换手写工具

- uuid v7 替换手写 RFC9562 实现（uuid@11.1.1 转为直接依赖）
- node:timers/promises setTimeout 替换两处手写 sleep（钉钉限流、AI 上游重试退避）
- dayjs 替换 4 处零散 Date 格式化（imports/expenses/occupancies 导入模板、档案报告日期）

apps/server/src/organizations/organizations.service.ts

@@ -1,7 +1,7 @@
 import { BadRequestException, Injectable, NotFoundException } from '@nestjs/common';
 import { InjectRepository } from '@nestjs/typeorm';
 import { Not, Repository } from 'typeorm';
-import { uuidV7 } from '../common/uuid-v7';
+import { v7 as uuidV7 } from 'uuid';
 import { Organization } from '../entities/organization.entity';
 import { Student } from '../entities/student.entity';
 import { Occupancy } from '../entities/occupancy.entity';