[BE-51] Add in-app notification entity and endpoints

[mftee]

Overview

Email notifications exist but there is no in-app notification system. Users need a persistent notification history they can read and dismiss.

Endpoints to Implement

Method	Path	Description
GET	/api/notifications	List notifications for current user
PATCH	/api/notifications/:id/read	Mark a notification as read
PATCH	/api/notifications/read-all	Mark all notifications as read
DELETE	/api/notifications/:id	Delete a notification

Acceptance Criteria

• Notification entity: id, userId, type, title, body, isRead, createdAt
• Notifications created automatically on: document verified, risk flag detected, job failed
• Unread count included in list response (meta.unreadCount)

[harouns-ux]

@harouns-ux has applied to work on this issue as part of the Stellar Wave Program's 3rd wave.

Kindly assign me this issue. I can quickly resolve them and integrate it into existing systems. I am software developer with 3 years experience.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @harouns-ux to this issue.

[drips-wave]

Congratulations, @harouns-ux! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on March 30, 2026.

🧑‍💻 @harouns-ux: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

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[drips-wave]

This issue has been completed by @harouns-ux as part of the Stellar Wave Program's 3rd Wave 🥳

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