[Frontend] Replace legacy auth screens with wallet verification

[Kaylahray]

Description

The login and register routes still expose a legacy wallet-signature flow instead of the modern Auth.js and SEP-10 challenge flow the app already documents.

User Story

As a wallet user,
I want to sign in and register through a real wallet verification flow,
so that my session is secured by an actual Stellar signature.

Requirements and Context

• Files: app/(auth)/login/page.tsx, app/(auth)/register/page.tsx, app/components/wallet-login-form.tsx, app/app/api/auth/challenge/route.ts, app/app/api/auth/verify/route.ts
• Remove the legacy mock signature flow from the UI
• Use the challenge and verify endpoints as the canonical authentication path
• Ensure the UX makes it clear when a user is logging in versus registering

Suggested Implementation

// AUTH FLOW
// 1. Request a challenge from /api/auth/challenge.
// 2. Ask the wallet to sign the challenge.
// 3. Submit the signed payload to /api/auth/verify.
// 4. Redirect the user after a successful session is created.

Acceptance Criteria

• Login and registration both use the real wallet verification flow.
• The legacy mock signature logic is no longer surfaced in the UI.
• Failed signatures are shown with a clear user-facing error.

Submission Guidelines

• Branch: feat/wallet-auth-ui
• Depends on: POST /api/auth/challenge and POST /api/auth/verify
• PR: feat(frontend): switch auth screens to challenge-based wallet login

[code-0-stella]

@code-0-stella has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

Hey, I would like to be assigned to this issue. I will replace the legacy mock wallet-signature flow with the real SEP-10/Auth.js challenge-based authentication flow, integrate the challenge and verify endpoints into both login and registration screens, improve the UX distinction between sign-in and sign-up, and add clear error handling for failed signature verification.

Can I be assigned to this issue?

ℹ️ Repo Maintainers: To accept this application, review their application or assign @code-0-stella to this issue.

[SaintSammi]

@SaintSammi has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

I want to work on this pls

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

[drips-wave]

Congratulations, @SaintSammi! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 2, 2026.

🧑‍💻 @SaintSammi: 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 🌊