[CT-22] Scaffold credential_badge contract — define Badge and Credential types

[yusuftomilola]

Overview

Create scaffolding for the credential_badge Soroban contract inside contracts/sandbox/credential_badge/. This contract lets the hub issue verifiable on-chain badges to members.

Acceptance Criteria

• Cargo.toml created with correct Soroban SDK dependency
• src/types.rs defines BadgeType (id, name, description, created_at), Credential (badge_type_id, holder, issued_at, issuer, is_revoked)
• src/errors.rs defines: AdminNotSet, AlreadyInitialized, Unauthorized, BadgeTypeNotFound, CredentialNotFound, AlreadyIssued, CredentialRevoked
• DataKey enum covers: Admin, BadgeType(String), BadgeTypeList, Credential(String, Address), HolderCredentials(Address)
• initialize is stubbed
• Code compiles with cargo build

[feromoneth]

@feromoneth has applied to work on this issue as part of the Stellar Wave Program's 4th wave.

Hello Maintainer, Good day
I'd like to take this issue on. I've reviewed the relevant modules and understand the expected behaviour.
I can implement a clean and maintainable fix aligned with the existing architecture and testing standard.

Would proceed with implementation immediately once assigned

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

[Thommyy7]

@Thommyy7 has applied to work on this issue as part of the Stellar Wave Program's 4th wave.

can i work on this?

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Thommyy7 to this issue.

[drips-wave]

Congratulations, @Thommyy7! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on April 29, 2026.

🧑‍💻 @Thommyy7: 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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[drips-wave]

This issue has been completed by @Thommyy7 as part of the Stellar Wave Program's 4th Wave 🥳

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