Add payment header redaction helper tests

[emrekayat]

Goal

Ensure logs and debug output never expose payment proof headers by accident.

Scope

• Find the smallest existing place to add a redaction helper or tests for redacting sensitive headers.
• Cover payment, payment-response, and authorization style header names case-insensitively.
• Preserve non-sensitive headers used for debugging.
• Avoid changing request handling behavior.

Acceptance criteria

• Sensitive payment/auth headers are redacted in the tested helper/output.
• Header matching is case-insensitive.
• Non-sensitive headers remain visible.
• npm test --workspace @query402/api targeted to the new/updated test passes.
• npm run typecheck --workspace @query402/api passes.

Notes

Keep this small and test-driven. If no helper exists, introduce a tiny local utility rather than a broad logging redesign.

[annacodervibe]

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

I would like to work on this issue. I have experience with Rust and Soroban smart contract development. I will follow the acceptance criteria and add tests. Excited to contribute. Kindly assign.

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

[drips-wave]

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

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