Add Notification Dead-Letter Handling

[Abd-Standard]

Description

Introduce a mechanism for isolating notifications that repeatedly fail delivery so they do not indefinitely block normal processing.

Acceptance Criteria

Repeatedly failed notifications can be isolated.

Dead-lettered notifications remain traceable.

Operators can inspect failure reasons.

Normal notification processing continues.

[Emmyranky]

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

Hi maintainer, I would like to work on this issue

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

[drips-wave]

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

🧑‍💻 @Emmyranky: 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.

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