[Backend] -- Implement User Preference Management

[Devsol-01]

Description:
Create comprehensive user preference system for notifications, privacy, display settings, and communication channels.

Acceptance Criteria:

• Design preference schema
• Create preference CRUD APIs
• Add default preferences
• Implement preference validation
• Add preference categories
• Create preference migration system

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[keljoshX]

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

Hi maintainer, can i be pls assigned to to this

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

[Meme11030]

@Meme11030 has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

Hi solo I will like to work on this

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Meme11030 to this issue.

[drips-wave]

Congratulations, @Meme11030! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 2, 2026.

🧑‍💻 @Meme11030: 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

When opening a PR, please link it to this issue to ensure it gets tracked accurately. Points are awarded when this issue is marked as completed by the maintainer.

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