Add creator route 404 JSON helper

[Chucks1093]

Summary

Add a helper for returning consistent 404 JSON payloads for creator routes.

Acceptance Criteria

• helper sets status and response body consistently
• includes an error code from shared constants
• can be reused across creator endpoints

Contributor coordination: https://t.me/accesslayerorg

[Danitello123]

@Danitello123 has applied to work on this issue as part of the Stellar Wave Program's 3rd wave.

Hi
Please I would love to work on this issue

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[khanavi272-spec]

@khanavi272-spec has applied to work on this issue as part of the Stellar Wave Program's 3rd wave.

I would like to work on this issue

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[SamixYasuke]

@SamixYasuke has applied to work on this issue as part of the Stellar Wave Program's 3rd wave.

Hi maintainer, I'd like to handle this issue

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[drips-wave]

Congratulations, @Danitello123! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on March 30, 2026.

🧑‍💻 @Danitello123: 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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[Emelie-Dev]

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

Hi, I would love to work on this issue.

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