[MerchantRegistry] Add suspend_merchant function separate from update_merchant

[JayWebtech]

Overview

Suspending a merchant (e.g. for fraud) currently requires calling update_merchant(active: Some(false)) — but only the merchant itself can call update_merchant (it requires merchant auth). Admins cannot currently suspend a merchant.

Technical Requirements

• Implement suspend_merchant(admin: Address, merchant_id: Address, reason: String).
• Require admin auth and verify admin == stored_admin.
• Store suspension reason and timestamp on the Merchant struct.
• Ensure create_payment (in PaymentProcessor) checks that merchant is active and not suspended.
• Add reinstate_merchant for admin to lift suspension.

[Turawa2]

@Turawa2 has applied to work on this issue as part of the Stellar Wave Program's 3rd wave.

hello i can work on this project Assign me please!

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[Joewizy]

@Joewizy has applied to work on this issue as part of the Stellar Wave Program's 3rd wave.

gm, I’m a blockchain and backend engineer building production‑grade smart contracts and DeFi protocols. I’d love to work on this issue.

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

[drips-wave]

Congratulations, @Turawa2! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on March 30, 2026.

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