Add CI with test coverage

[nettee]

Summary

Add a CI workflow that runs the project's test suite on pull requests and pushes.

Scope

• Add a GitHub Actions workflow for CI.
• Install project dependencies in CI.
• Run the test command as part of the workflow.
• Ensure failures are surfaced clearly and block merging.

Acceptance Criteria

• CI runs automatically on pull requests.
• CI includes the test suite.
• A failing test causes the CI job to fail.

[nettee]

Looper finished work on this issue.

Pull request: #30

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