Implement donation CSV export

[ayshadogo]

User Story:
As a donor, I want to export my donation history as a CSV so that I can use it for tax records.
Acceptance Criteria:

• GET /users/me/donations/export?format=csv
• CSV columns: Campaign, Amount, Asset, Date, Tx Hash, USD Equivalent
• USD equivalent calculated at time of donation (cached price)
• Large exports processed via Bull queue

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[neyij]

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

hi, i would like to work on this.

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

[coderolisa]

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

Hello maintainer let me work on this
please assign

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[dDevAhmed]

@dDevAhmed 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

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

[drips-wave]

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

🧑‍💻 @dDevAhmed: 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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