Add contract address validation for project submissions

[Naomi-Gift]

Problem
Projects can be submitted with website and docs URLs, but there is no way to validate or display associated Stellar/Soroban contract addresses.
Suggested fix
Add optional contract address fields with Stellar/Soroban format validation and display them on project detail pages.
Acceptance criteria
Project submit/edit supports validated contract identifiers.
Invalid contract IDs are rejected client-side and service-side.
Project detail pages show contract metadata when available.

[Hunter-baddie]

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

Please can I be assigned this issue?

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Hunter-baddie 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.

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 🌊