[codex] add minimal GitHub Actions CI workflow

[stacknil]

Summary

This PR adds a minimal GitHub Actions CI workflow for the repository so every push and pull request runs the existing pytest suite automatically. It also adds a small README badge that points at the stable CI workflow.

Before this change, the telemetry-window-demo prototype had local tests but no repository-level automation to catch regressions in time parsing, sliding-window behavior, or rule-based alert logic when changes landed in GitHub. The underlying issue was simply missing CI wiring rather than a code defect.

The fix keeps scope intentionally small for a portfolio prototype:

• add .github/workflows/ci.yml
• trigger on push and pull_request
• run one test job on ubuntu-latest
• use actions/setup-python@v5 with Python 3.11
• upgrade pip, install the project with dev dependencies via python -m pip install -e ".[dev]"
• run pytest
• avoid deployment, release, and packaging steps

Validation

• pytest