[BACKEND] Implement POST /v1/admin/issuers endpoint

[dev-fatima-24]

Priority: high

Description

An admin-only endpoint to authorize a new healthcare provider by invoking the contract's add_issuer function. Required for onboarding new issuers without manual contract calls.

Acceptance Criteria

• POST /v1/admin/issuers accepts { wallet_address } in the body
• Endpoint requires a valid admin JWT (role: admin)
• Contract add_issuer is invoked with the admin secret key
• Success returns 201 with the new issuer's wallet address
• Duplicate issuer returns 409

[Deyanju23]

@Deyanju23 has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

Hi maintainer, i can resolve this issue

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Deyanju23 to this issue.

[Amas-01]

@Amas-01 has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

Hello Maintainer,
I'll like to work on this Issue

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Amas-01 to this issue.

[drips-wave]

Congratulations, @Deyanju23! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 2, 2026.

🧑‍💻 @Deyanju23: 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

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