devops: Set up Slack integration for GitHub Actions CI failure notifications

[FaveTeamz]

Summary

CI failures are currently only visible in the GitHub Actions UI. Developers must check the GitHub interface proactively to know if their merge broke the build. There is no proactive notification to the team's Slack workspace.

Problem

A broken main branch can go unnoticed for hours if no one checks the GitHub Actions dashboard. This blocks other developers from merging their own PRs without knowing the build is already red.

Acceptance Criteria

• Add a notify-slack reusable workflow that posts to a configurable Slack channel
• Trigger on: CI failure on main branch (backend, frontend, contract CI workflows)
• Message includes: workflow name, commit SHA (truncated), author, commit message (first line), link to failing run
• Use a Slack Incoming Webhook URL stored in GitHub Actions secrets as SLACK_WEBHOOK_URL
• Do not post on PR failures — only on merges to main
• Add a green Build restored message when a previously failing build passes again
• Document setup in docs/ci-cd.md

[prodbydeco]

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

Hello maintainer,
I have a vast experience in solving github issues.
Please do well to assign me this let me get it done for you
Thank you.

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[samuelelijah585]

@samuelelijah585 has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hello, I've reviewed the issue and its acceptance criteria, and I'm confident I can deliver a solution that meets the requirements. I'd appreciate it if you could assign this issue to me. Thank you!

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[soterika]

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

hello maintainer i will like to work on this issue

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[OmniZlatoon]

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

Good day sir/ ma'am, I have 5 years of experience working on tasks like this and handling similar challenges across backend, frontend, and smart-contract development. I have carefully read and fully understood the task requirements, and I am confident I can deliver a clean, efficient, and well-tested solution promptly. I always ensure high-quality implementation, maintainability, and adherence to best practices.

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[To0yeni]

@To0yeni has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

I am an experienced software engineer and I can deliver on time.

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[kaizercodes]

@Kaizer4show has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hi, i would like to work on this issue

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[drips-wave]

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

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[drips-wave]

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

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