Add regression test for creator registration with minimum valid handle length

[Chucks1093]

Summary
Handle validation is tested at the maximum and empty-string boundaries, but not at the minimum valid length. A regression test at the minimum valid length confirms the validation accepts the shortest allowed handle without error.

Scope

• add a regression test that registers a creator with a handle of exactly the minimum valid length
• assert the registration succeeds
• add a case with a handle one character below the minimum and assert it is rejected

Acceptance Criteria

• a handle at the minimum valid length registers successfully
• a handle one character below the minimum is rejected with the correct error
• the minimum length value is referenced from the defined constant

Contributor coordination: if you pick this up, reach out in Telegram for updates or clarification: https://t.me/accesslayerorg

[khanavi272-spec]

@khanavi272-spec has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

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[shadrach68]

@shadrach68 has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

please assign this issue to me.

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Congratulations, @shadrach68! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 2, 2026.

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