Add email preference center with granular unsubscribe management

[nanaf6203-bit]

Problem

UserPreferences model has emailNotifications toggle but no granular email type preferences, unsubscribe from specific types, preference center endpoint, or unsubscribe link tracking.

Expected Outcome

Granular email preferences with unsubscribe management.

Acceptance Criteria

• Preference center endpoint (GET/PUT /users/me/email-preferences)
• Granular toggles per email type
• One-click unsubscribe links
• Unsubscribe token for email-based opt-out

Files Affected

src/users/user-preferences.service.ts

Difficulty

Easy

Estimated Effort

Small (2-3 days)

Labels

email, ux, feature

[Timmytaps-1]

@Timmytaps-1 has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

Hi Maintainer, I’m interested in working on this issue and will open a PR with a complete solution.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Timmytaps-1 to this issue.

[ValJnr-dev1]

@ValJnr-dev1 has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

Hi Maintainer,

I’m a smart contract and full-stack developer and would love to contribute to this issue. I’m an experienced contributor with hands-on expertise in Rust, Soroban, Cairo, and TypeScript.

I’m passionate about building secure, scalable blockchain solutions, with a strong emphasis on writing clean and maintainable code. Based on the scope of this issue, I’m confident I can deliver a complete solution within 24 hours of assignment.

I’d greatly appreciate the opportunity to contribute and help move this forward.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @ValJnr-dev1 to this issue.

[Nimatstar]

@Nimatstar has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

Hi can i work on this task?

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

[drips-wave]

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

🧑‍💻 @Nimatstar: 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 @Nimatstar as part of the Stellar Wave Program's 7th Wave 🥳

😎 @Nimatstar: You earned 200 Points for completing this issue! After the current Wave ends, you'll be eligible for a percentage of the Wave's reward pool based on the percentage of total points you've earned. Learn more here. You can also Leave a review to share your experience working on this issue.

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