feat(email): add mock Resend mode

[Ekenesamuel8]

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.

Testing

Commands run:

npm run lint
npx tsc --noEmit
npm run build

Screenshots / demo

Add screenshots or screen recordings for UI changes.

Notes for maintainers

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

close #25

[Obiajulu-gif]

@Ekenesamuel8 great work , fix your lint error