Add End-to-End Notification Pipeline Tests

[Abd-Standard]

Description:
Create an end-to-end test covering the complete NotifyChain workflow from event ingestion to notification delivery.

Flow:

Blockchain Event → Listener → Validation → Database → Scheduler → Notification

Acceptance Criteria:

The complete workflow executes successfully in a test environment.
Failure at each major stage is handled predictably.

[pimaster900]

@pimaster900 has applied to work on this issue as part of the Stellar Wave Program's 9th wave.

I would like to work on this issue.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @pimaster900 to this issue.

[MaybeSomeone-arc18]

@MaybeSomeone-arc18 has applied to work on this issue as part of the Stellar Wave Program's 9th wave.

Tree-checked: notification-flow-e2e starts at notification creation; the front of the chain named here - blockchain event ingestion through listener validation into the database - is exercised in no test. Plan: a full-chain e2e injecting a synthetic Stellar event at the listener boundary with only the final webhook mocked, plus per-stage failure rows asserting predictable handling at validation, persistence, and delivery. I know this tree hands-on: four merge-damage repairs plus a lockfile resync committed on my working branch. I will implement and run everything locally before opening the PR.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @MaybeSomeone-arc18 to this issue.

[drips-wave]

Congratulations, @pimaster900! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on September 30, 2026.

🧑‍💻 @pimaster900: 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.

🌊 Happy Wave 🌊

[grantfox-oss]

🎉 This issue has been marked as completed on GrantFox!

@pimaster900's PR #930 was approved and merged by @Abd-Standard.

🏆 @pimaster900: You earned 35 FoxPoints for this contribution! Your current tier: Explorer (271 total points). Track your full progress on GrantFox.

👏 Great work, @pimaster900! Keep contributing to Core-Foundry.