Backend: Add campaign metrics CSV/JSON export endpoint

[joelpeace48-cell]

Summary

Campaign operators need to export their data for reporting, accounting, and off-platform analysis. A downloadable export of campaign stats, participants, and reward distributions covers the most common operator use cases.

Acceptance Criteria

• Add GET /api/v1/campaigns/:id/export?format=csv|json (API key required)
• CSV export includes columns: participantAddress, registeredAt, pointsCredited, pointsClaimed, netPoints, referredBy
• JSON export is the same data in { campaign: {...}, participants: [...] } structure
• Streaming response for large exports (don't buffer entire dataset in memory) — use Node.js stream pipeline
• Set appropriate headers: Content-Disposition: attachment; filename=campaign-{id}-export.csv
• Add date range filter: ?from=ISO_DATE&to=ISO_DATE
• Rate limit: max 5 exports per campaign per hour
• Audit log entry on each export
• Unit tests for CSV format, JSON format, streaming, rate limit

References

• backend/src/index.js
• backend/src/dal/

[Chigybillionz]

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

let me fix this. pr submission within 8hrs. thank you

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

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[directorfloo]

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

I will love to work on this is issue, please assign it to me

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[Jokay1997]

@Jokay1997 has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

Hi maintainer, I would love to take on this issue. I’ve reviewed it and I know it is something I can work on. I have an experience with Rust, Soroban smart contracts and other programming languages.

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[BigJohn-dev]

@BigJohn-dev 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 it aligns closely with the kind of engineering problems I enjoy solving — building reliable, maintainable, and user-focused software. I’m particularly interested in contributing to real-world systems where code quality, scalability, and thoughtful implementation matter.

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[Timothy2025-20]

@Timothy2025-20 has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

Hi maintainer, I will like to resolve this issue if assigned to me. Thank you 🙏

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