[BE-10] Implement auth register endpoint (POST /auth/register)

[yusuftomilola]

Overview

Implement the user registration endpoint inside backend/contrib/. This is the first step in the auth flow.

Location

All work must be inside backend/contrib/src/auth/.

Acceptance Criteria

• POST /auth/register endpoint implemented
• RegisterDto with fields: firstName, lastName, email (@IsEmail), password (min 8 chars)
• Password hashed with bcrypt (10 rounds) before storing
• Returns { accessToken, refreshToken, user } on success
• Throws ConflictException (409) if email already exists
• Refresh token hashed and stored in the database

[feromoneth]

@feromoneth has applied to work on this issue as part of the Stellar Wave Program's 4th wave.

Hello Maintainer, Good day
I'd like to take this issue on. I've reviewed the relevant modules and understand the expected behaviour.
I can implement a clean and maintainable fix aligned with the existing architecture and testing standard.

Would proceed with implementation immediately once assigned

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

[temiport25]

@temiport25 has applied to work on this issue as part of the Stellar Wave Program's 4th wave.

can i work on this?

ℹ️ Repo Maintainers: To accept this application, review their application or assign @temiport25 to this issue.

[drips-wave]

Congratulations, @temiport25! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on April 29, 2026.

🧑‍💻 @temiport25: 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.

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[drips-wave]

This issue has been completed by @temiport25 as part of the Stellar Wave Program's 4th Wave 🥳

😎 @temiport25: You earned 200 Points for completing this issue! After the current Wave ends, you'll be eligible for a percentage of the Wave's reward pool based on the percentage of total points you've earned. Learn more here. You can also Leave a review to share your experience working on this issue.

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