backend: Implement dead letter queue for failed webhook notifications

[ONEONUORA]

Description

Move permanently failing push/webhook dispatches to DLQ table after 5 retries.

Files to Edit/Create

• backend/src/services/notifications.rs

Acceptance Criteria

• Store failure payload and error message in failed_webhook_dlq table.

Guidance / Hints

Record retry counts and error reason.

[Tundeakinbami-dev]

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

i would like to work on this issue

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[Bigdaddyobamo]

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

Good afternoon, Maintainer. Please have this issue on my desk.

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[success-OG]

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

Hello repo maintainer.. Can i work on this..

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[tali-creator]

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

hi boss can i work on this

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