Testing: Implement comprehensive integration test suite

[supreme2580]

Description
Ensure system reliability through automated end-to-end tests.

Scenarios

• Happy path: Registration -> Payment -> Confirmation -> Mint.
• Error paths: Invalid signatures, insufficient balances, rate limits.
• Use Jest and Supertest.

[devJaja]

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

Hello, I am a smart contract and full-stack developer with experience across 30+ blockchain projects, including development within the Stellar ecosystem. I am interested in contributing to this issue and bringing my expertise to support its completion.

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

[drips-wave]

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

🧑‍💻 @devJaja: 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.

Warning

When opening a PR, please link it to this issue to ensure it gets tracked accurately. Points are awarded when this issue is marked as completed by the maintainer.

🤠 Repo maintainers: Please keep an eye on the contributor's progress and review their work before the due date. You can manage this issue, including adjusting its complexity and points, here.

🌊 Happy Wave 🌊

[drips-wave]

This issue has been completed by @devJaja as part of the Stellar Wave Program's 3rd Wave 🥳

😎 @devJaja: 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.

🧑‍💻 Repo maintainers: How'd the contributor do? Leave a review to share your experience working with them.