docs: add Stellar asset & Soroban contract design document

[Chidubemkingsley]

Summary

What changed?

Area changed

Check all that apply:

• Frontend / UI
• Backend / API routes
• Auth / Privy
• Payments / Paystack
• Email / Resend
• Stellar / Soroban
• MongoDB models
• Documentation
• Tests
• Security

Contributor safety checklist

• I did not commit .env.local or real secrets.
• I did not expose server-only variables in client-side code.
• I used mock mode or my own sandbox/test credentials.
• I did not add deployment steps for contributor PRs.
• I did not add maintainer-only credentials.

Screenshot/demo

Testing

Commands run:

npm run lint
npx tsc --noEmit
npm run build

• closes [STELLAR] Document vehicle pool asset issuance and Soroban contract interfaces #29

Notes for maintainers

Mention anything that needs special review, migration, or follow-up.

[Obiajulu-gif]

Thanks for the contribution! This looks like a useful improvement, and I appreciate you taking the time to work on it.

I noticed the PR template has a Screenshots / demo section for UI changes, but it’s currently empty.

Could you please attach a few screenshots or a short screen recording showing the changes? It will make the review process much easier and help us verify the user experience.

[Obiajulu-gif]

Resolve your CI errors also

[Obiajulu-gif]

@Chidubemkingsley saw the quality of work you did there. that great