refactor(architecture): split the 796-line auth_handler.go into focused sub-handlers

[cypriannwokolo2-creator]

Summary

internal/api/handler/auth_handler.go (796 lines) implements 20+ auth flows in one file: register/verify, login, passkey, TOTP, recovery, sessions, wallet init, nonce. It also contains wallet-seed derivation and passkey-pepper helpers (lines 734-766) that belong in a domain service.

Acceptance Criteria

• Split into focused handlers (registration, passkey, totp, recovery, sessions, wallet-init)
• Move crypto/seed-derivation helpers into the wallet/auth domain services
• No change to public route/response contracts
• Existing auth tests + integration tests pass

Complexity

High — broad surface, must preserve HTTP contracts.

[Chinonso-Peter]

@Chinonso-Peter has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Can i work on this issue

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

[drips-wave]

Congratulations, @Chinonso-Peter! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on August 31, 2026.

🧑‍💻 @Chinonso-Peter: 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 🌊