feat(ci-server): set commit status via GitHub REST API

[HotFazz]

Description

Implement commit status notifications in the CI server so that GitHub shows pending, success, or failure for each build.

Expected outcome

The CI server supports notification of CI results.

Acceptance criteria

• REST API is used to set commit status
• The CI server sets the commit status
• Set status to pending when the build starts
• Set status to success or failure when it finishes
• Pushing a passing commit shows ✅ on GitHub
• Pushing a failing commit shows ❌ on GitHub
• Status is set to pending ( ⏳ ) while the build runs
• Include a target_url pointing to the build details page (related to feat: serve build history web pages #19)
• Unit tests mock the GitHub API call and verify correct payload
• How notification has been implemented and unit-tested is documented in README.md
• Statement of contribution is added on the repository root

Related

ref: #19