[Backend] Replace simulated wallet withdrawals with Stellar settlement

[Kaylahray]

Description

The withdrawal route still returns a placeholder for the on-chain flow and only decrements the local balance in simulated mode.

User Story

As a wallet user,
I want to withdraw funds to a real Stellar destination,
so that I can move value off-platform when needed.

Requirements and Context

• Files: app/app/api/wallet/withdraw/route.ts, app/lib/sep10.ts, app/lib/prisma.ts
• Build and submit a real Stellar payment transaction when simulated=false
• Persist the pending and completed withdrawal states correctly
• Surface on-chain submission failures with useful errors

Suggested Implementation

// WITHDRAW ROUTE
// 1. Build the Stellar payment transaction.
// 2. Submit it to the network.
// 3. Store the withdrawal record with chain metadata.
// 4. Update local balance only after a valid settlement path.

Acceptance Criteria

• The non-simulated withdrawal path no longer returns a placeholder error.
• Successful withdrawals are reflected in wallet history.
• Balance changes are consistent with the transaction result.

Submission Guidelines

• Branch: feat/stellar-withdrawals
• Depends on: Stellar submission utilities
• PR: feat(backend): settle wallet withdrawals on Stellar

[morapay-app]

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

I’d like to work on this issue because it replaces the current simulated withdrawal flow with a real Stellar settlement process, which is essential for making the wallet fully functional in production.

I can integrate proper Stellar transaction construction and submission when simulated=false, persist withdrawal state with correct pending/completed tracking, and ensure errors from on-chain submission are surfaced clearly while keeping balance consistency and transaction history accurate.

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

[phertyameen]

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

Hi, I will like to work on this issue.
I have an eta of 12 hrs

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

[drips-wave]

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

🧑‍💻 @phertyameen: 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 🌊