feat(backend): Implement transaction status webhook fan-out

[Viky207]

Problem

Transaction status changes not broadcast to webhooks.

Task

Implement event fan-out.

Acceptance Criteria

• Events: payment.initiated, settled, failed, refunded
• Fan-out filtered by event type
• Retry with backoff
• DLQ for failures
• Background via JobQueueModule
• Deduplicated by eventId

[Fabulouz34]

@Fabulouz34 has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hi maintainer please I will appreciate it if I'm given this issue to work on. Please assign me I'm ready to get started
Thank you

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Fabulouz34 to this issue.

[abbys-code-hub]

@abbys-code-hub has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

HI, can I work on this issue.I’d implement reliable webhook fan-out with event filtering, retries, DLQ handling, and eventId deduplication through the existing JobQueueModule.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @abbys-code-hub to this issue.

[kceeglo345-dev]

@kceeglo345-dev has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

I would love to work on this issue

ℹ️ Repo Maintainers: To accept this application, review their application or assign @kceeglo345-dev to this issue.

[drips-wave]

Congratulations, @kceeglo345-dev! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on August 31, 2026.

🧑‍💻 @kceeglo345-dev: 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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