[Backend] Add notification delivery fan-out

[Kaylahray]

Description

Notifications are retrievable, but there is no richer delivery pipeline for fan-out, live updates, or prioritized notification types.

User Story

As a user,
I want to receive timely notifications for important actions,
so that I do not miss replies, likes, entries, or moderation events.

Requirements and Context

• Files: app/app/api/notifications/route.ts, app/app/api/notifications/[id]/route.ts, app/lib/notifications.ts
• Add a delivery layer that can fan out new notifications from core events
• Support unread counts, read state, and prioritized delivery types
• Make the API suitable for polling today and live transport later

Suggested Implementation

// NOTIFICATIONS DELIVERY
// 1. Create notifications from source events.
// 2. Persist read/unread state consistently.
// 3. Expose unread counts and recent activity.
// 4. Keep the payload ready for realtime transport later.

Acceptance Criteria

• Notification creation can be triggered from product events.
• Unread/read state remains consistent.
• The delivery layer is reusable for future realtime transport.

Submission Guidelines

• Branch: feat/notification-fanout
• Depends on: notification storage and event sources
• PR: feat(backend): add notification fan-out and delivery layer

[kingeligma]

@kingeligma has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

Hi I am Isaiah a Softare dev and would love to solve your issue

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

[morapay-app]

@morapay-app has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

I’d like to work on this issue because a solid notification delivery layer is important for user engagement and future realtime features. I can implement a reusable fan-out system that handles notification creation, unread/read consistency, and prioritized delivery while keeping the API structured for both polling now and websocket or push-based transport later.

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

[KuchiMercy]

@KuchiMercy has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

Hi maintainer, I'd like to work on this issue. Can you assign?

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

[drips-wave]

Congratulations, @KuchiMercy! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 2, 2026.

🧑‍💻 @KuchiMercy: 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.

Warning

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