No `If-Match` / `ETag` support for optimistic concurrency on wallet operations

[Junman140]

src/controllers/walletController.ts: Wallet balance updates are not conditioned on an ETag or version number. Two concurrent requests (e.g., a transfer and a sweep) may both read the same balance and both write, causing lost updates.

[Banx17]

@Banx17 has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Good day Team, I would love to work with you on this issue, please kindly assign thanks.

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[drips-wave]

Congratulations, @Banx17! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 30, 2026.

🧑‍💻 @Banx17: 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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[grantfox-oss]

🎉 This issue has been marked as completed on GrantFox as part of the Official Campaign campaign!

@Banx17's PR #545 was approved and merged by @Junman140.

🏆 @Banx17: You earned 35 FoxPoints for this contribution! Your current tier: Explorer (436 total points). Track your full progress on GrantFox.

👏 Great work, @Banx17! Keep contributing to Pi-Defi-world.

[drips-wave]

This issue has been marked as completed by a Drips Wave moderator for @Banx17 as part of the Stellar Wave Program's 6th Wave 🥳

Moderator's reason: [Auto-assessed] The contributor successfully implemented optimistic concurrency control for wallet operations as requested. The PR was reviewed and merged by the maintainer, addressing the core issue with a robust versioning system, new services, and unit tests.

😎 @Banx17: 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.

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ℹ️ Note: This issue was marked complete via moderation. Points were issued even though the GitHub issue remains open.