[CT-14] Build VerificationWebhookNotifier

[mftee]

Problem

When a document hash is successfully anchored or verified on Stellar, no external system is notified. Integrators who need to react to on-chain confirmation events must poll the API continuously.

Proposed Solution

Create a VerificationWebhookNotifier inside contract/module/webhook/ that sends an HTTP POST notification to a configured webhook URL after each successful Stellar operation.

Acceptance Criteria

• Reads the WEBHOOK_URL environment variable on startup — if not set the notifier is disabled and logs a warning
• notify(event_type: &str, document_hash: &str, tx_hash: &str, timestamp: i64) async function fires a POST request to the configured URL
• Webhook payload is JSON: { event_type, document_hash, tx_hash, timestamp, service: smalda-contract }
• The submit, revoke, and transfer handlers call the notifier after a successful Stellar transaction
• Uses reqwest with a 5-second timeout — failed webhook deliveries are logged at WARN level but do not cause the handler to return an error
• Retries the webhook delivery once after a 2-second delay on the first failure before giving up
• Implementation files live inside contract/module/webhook/

[Oluwasuyi-Timilehin]

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

Hello maintainers I'm a full stack developer with experience in building scalable systems I can handle this perfectly if assigned

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

[lekanay2005-coder]

@lekanay2005-coder has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hello, I’ve gone through the requirements and I’m confident I can implement a proper solution that matches the acceptance criteria. Kindly assign this issue to me.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @lekanay2005-coder to this issue.

[Imole203]

@Imole203 has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

I will love to work on this issue,pls 🙏 give me

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Imole203 to this issue.

[Silver36-ship-it]

@Silver36-ship-it has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

I would love to work on this professionally, please assign it to me

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Silver36-ship-it to this issue.

[Ibinola]

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

I'd like to work on this task.

My approach: ## Problem When a document hash is successfully anchored or verified on Stellar, no external system is notified. Integrators who need to react to on-chain confirmation events must poll the API continuously. ## Proposed Solution

I'll add tests and documentation as part of the PR.

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

[grantfox-oss]

🦊 GrantFox — @Ibinola has been assigned to this issue!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #546)
2. Your PR will be reviewed by the CodeGirlsInc maintainers

Good luck! Track your progress on GrantFox.

[drips-wave]

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

🧑‍💻 @Ibinola: 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!

@Ibinola's PR #593 was approved and merged by @mftee.

🏆 @Ibinola: You earned 35 FoxPoints for this contribution! Your current tier: Explorer (646 total points). Track your full progress on GrantFox.

👏 Great work, @Ibinola! Keep contributing to CodeGirlsInc.