Add Contract API Compatibility Tests

[Naomi-Gift]

Public APIs can accidentally change signatures. The project needs tests or tooling to detect breaking interface changes.
Acceptance criteria:
Generate and store contract interface/spec artifact.
CI fails when public API changes unexpectedly.
Document how to intentionally update the spec.
Tests or scripts cover artifact generation.

[Henrichy]

@Henrichy has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hello Sir,
I came across your project and I’m really interested in contributing.
I have experience with React for building responsive, user-friendly interfaces, and I’m also familiar with smart contracts and blockchain basics. I focus on writing clean, scalable code and improving user experience.
I’m a fast learner and ready to get started immediately. Please let me know the next steps.
Thank you.
Best regards,
Henry

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

[drips-wave]

Congratulations, @dev-chinasa! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 30, 2026.

🧑‍💻 @dev-chinasa: 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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