AmazonOA #9

MovieDB(MERN): Actor Follow & Notification System

估计中等非算法题评测数据准备中，可先阅读题面

考点（AI 标注）模拟/实现迭代器设计

实现 follow actor + 收到新片上映通知:

POST /api/follow body {actorId}
GET /api/notifications/ (列分页)
GET /api/notifications/unread-count
PUT /api/notifications/:id/read
Admin POST /api/admin/movies + POST /api/admin/movies/:id/launch (触发通知 fan-out)

考点: Notification fan-out 在 movie launch 时遍历所有 followers + insertMany.