Add creator param not-found shortcut helper

[Chucks1093]

Summary

Add a small helper for quickly returning a not-found result from creator param checks.

Scope

• keep creator not-found shortcut logic in one place
• reduce repeated route-level boilerplate
• make the helper reusable across creator endpoints

Acceptance Criteria

• creator param not-found behavior can be reused
• route handlers become simpler where adopted
• helper stays small and predictable

Contributor note: comment on the issue first and reach out in Telegram for updates or coordination: https://t.me/accesslayerorg

[Belzabeem]

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

I believe i can work on this issue and submit a pr before the end of the day

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

[drips-wave]

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

🧑‍💻 @Belzabeem: 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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