[P2] Encryption: Migrate existing plaintext on-chain subscriptions to encrypted format

[Calebux]

Parent Issue

#824

Summary

Build a migration tool/script that reads existing plaintext subscriptions from the SubscriptionRegistry, encrypts them, and re-stores them.

Details

• One-time migration script run by each user (since encryption requires their key)
• Flow: read all user's plaintext subs → derive encryption key → encrypt each → call store_encrypted_subscription → optionally clear plaintext fields
• Must handle partial migration (resume after failure)
• Could be triggered from Settings → Privacy → "Encrypt my on-chain data"

Affected Code

• New: client/app/settings/privacy/migrate-encryption/ — UI component
• backend/src/services/blockchain-service.ts — migration logic
• client/lib/stellar-wallet.ts — key derivation for migration

Acceptance Criteria

• Migration is idempotent (safe to re-run)
• Progress indicator shown during migration
• Plaintext data is cleared after successful encryption
• Migration can resume after interruption

[VictorEzenma]

@VictorEzenma has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hello, I would love to contribute by applying the necessary fixes and improvements to get the work done

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

[drips-wave]

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

🧑‍💻 @VictorEzenma: 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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