Add API contract documentation for services

[Naomi-Gift]

Problem

Services expose project, review, wallet, Stellar, and Soroban behavior, but there is no contract documentation for expected inputs, outputs, and errors.

Suggested fix

Document service contracts in markdown or generated API docs.

Acceptance criteria

• Each service has documented methods and error cases.
• UI expectations for each service are clear.
• Mock and production behavior differences are documented.

[S4V10N]

@S4V10N has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

Hello, I would love to write the API contract documentation for your project. I have experience writing excellent articles and I can confidently craft one that meets all the specifications

ℹ️ Repo Maintainers: To accept this application, review their application or assign @S4V10N to this issue.

[drips-wave]

Congratulations, @S4V10N! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on July 30, 2026.

🧑‍💻 @S4V10N: 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 🌊