[BE-57] Implement per-user notification preferences — control channels per event type

[yusuftomilola]

Overview

Users should control which notifications they receive and through which channel. A user who handles checkouts daily may not want an email every time — just an in-app ping. This settings layer sits between the notification dispatcher (BE-56) and the actual delivery.

Context

• Depends on BE-55 and BE-56 (notification infrastructure)
• Preferences should default to all-enabled so new users get all notifications out of the box
• The notification preferences UI is built in FE-29

Acceptance Criteria

• Create NotificationPreference entity: id, userId, eventType (NotificationEvent from BE-56), emailEnabled (boolean, default true), inAppEnabled (boolean, default true), updatedAt
• GET /users/me/notification-preferences — returns all event types with current preference settings. If no record exists for an event type, return the default (both enabled)
• PUT /users/me/notification-preferences body: [{ eventType, emailEnabled, inAppEnabled }] — upserts all preferences in a single request
• Modify NotificationDispatchService from BE-56 to check preferences before dispatching: await preferenceService.shouldSend(userId, eventType, channel)
• POST /users/me/notification-preferences/reset — resets all preferences to default (all enabled)

[Henrichy]

@Henrichy has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hi! I'd like to work on this issue.
I've contributed to Rust, TypeScript, backend, frontend, and smart contract projects, with a focus on delivering focused, well-tested changes. I'll keep the implementation within the requested scope, preserve existing behavior unless the issue requires otherwise, include the necessary tests and documentation, and submit a PR that's straightforward to review.
Portfolio: https://henrichy-2gdu.onrender.com • ETA: ~2–4 hours.

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

[NickiM84]

@NickiM84 has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hello, I'm a fullStack developer with years of experience, I have worked on several projects, can I please work on this

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[Nimatstar]

@Nimatstar has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hi can i work on this task?

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[drips-wave]

Congratulations, @Nimatstar! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 30, 2026.

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