BA-105 — Add notification deduplication keys

[MaryammAli]

• Type: Reliability
• Affected area: notification providers/service
• BackendAcademy
• Summary: Retries and scheduled jobs can send duplicate reminders or alerts.
• Acceptance criteria: A deterministic event key prevents duplicates within a documented window; provider retries remain safe.

[supreme2580]

@supreme2580 has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hello maintainer, can I be assigned to this issue?

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[ustaxs]

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

I have read the requirements of this issue and i am confident that i can solve this

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[drips-wave]

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

🧑‍💻 @ustaxs: 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 Third Campaign campaign!

@ustaxs's PR #741 was approved and merged by @MaryammAli.

🏆 @ustaxs: You earned 40 FoxPoints for this contribution! Your current tier: Builder (1,268 total points). Track your full progress on GrantFox.

👏 Great work, @ustaxs! Keep contributing to BlockDash-Studios.

[drips-wave]

This issue has been completed by @ustaxs as part of the Stellar Wave Program's 8th Wave 🥳

😎 @ustaxs: 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. You can also Leave a review to share your experience working on this issue.

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