[CT-23] Implement badge type registration (admin)

[yusuftomilola]

Overview

Implement register_badge_type so the admin can define badge categories (e.g., "Top Contributor", "30-Day Streak"). Work inside contracts/sandbox/credential_badge/.

Acceptance Criteria

• register_badge_type(env, caller, id, name, description) is admin-gated
• Returns error if badge type ID already exists
• Stores BadgeType and indexes in BadgeTypeList
• Emits a registration event
• Code compiles with cargo build

[Daveside9]

@Daveside9 has applied to work on this issue as part of the Stellar Wave Program's 4th wave.

Please can I take this?

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[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 🥳

😎 @Thommyy7: You earned 200 Points for completing this issue! After the current Wave ends, you'll be eligible for a percentage of the Wave's reward pool based on the percentage of total points you've earned. Learn more here. You can also Leave a review to share your experience working on this issue.

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