[Backend] Implement Notification Retry Queue

[Abd-Standard]

Description

Introduce a retry mechanism for notifications that fail due to temporary service interruptions.

Tasks
Create retry queue service.
Configure retry intervals.
Track retry attempts.
Log final failures.

Acceptance Criteria
Failed notifications are retried automatically.
Retry limits are respected.
Logs contain retry history.

[naninu123]

Hi, interested in contributing to this.

I have experience across Stellar OSS bounties through GrantFox with merged PRs in Core-Foundry/Notify-Chain, Flux-DeFi/LiquidFlow, StellarLend, and aid-linkk. I adapt quickly to different codebases.

Approach:

1. Study the issue and surrounding code
2. Implement focused changes following repo conventions
3. Test and submit a clean PR

Available to start right away!

[leocagli]

Interested in picking this up! Please assign me.

[jfaoie]

Hi maintainers, I'd like to work on this bounty. Could you please assign me before I start, per the bounty program process? I'll keep the change scoped to the issue and submit a tested PR.

[omosvico]

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

Hi can I be assigned to this issue?

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

[dev-chinasa]

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

Hii, i'd like to work on this issue

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

[drips-wave]

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

🧑‍💻 @dev-chinasa: 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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