Polish for job-readiness: tests, CI, deploy config, recruiter-friendly README

[Gavand1969]

Summary

A non-invasive polish pass aimed at how the repo reads to a hiring manager and how it behaves in CI / on a fresh checkout. No app behaviour was changed.

• Reproducible setup — pinned upper bounds in `requirements.txt` (`<2.0 / <7.0 / <3.0`), new `requirements-dev.txt` adding pytest + playwright, and `.streamlit/config.toml` so theme + headless server defaults travel with the repo (useful for Streamlit Community Cloud).
• Tests — new `tests/` package: data-layer schema + business invariants (`copq_usd <= lot_value`, tier/severity domains, no nulls in core columns), generator determinism, page-module compile smoke for all four pages plus `app.py`.
• CI — new `.github/workflows/ci.yml` runs pytest on Python 3.11 and 3.12, then boots Streamlit and waits for `/_stcore/health` to confirm the app actually starts.
• README — adds a Business Impact paragraph (puts the $85M COPQ / 11.85% headline in context for a non-technical reader), a Skills Demonstrated bullet list grouped by analytics / data eng / dashboarding / engineering practice, dedicated Deploy and Tests sections, virtual-env step in the run instructions, `gh repo clone` instead of raw HTTPS, and a CI badge.

Test Plan

• `pytest tests/ -v` — 12 passed locally
• `streamlit run app.py` — boots clean, `/_stcore/health` returns `ok` (HTTP 200)
• `python -m py_compile app.py pages/*.py src/data.py` — clean
• CI workflow run (will trigger on push)

Notes / Remaining Recommendations

These would be follow-ups, intentionally out of scope here:

• Live demo link on Streamlit Community Cloud (one-click deploy now that config is in place)
• A docker/Dockerfile for non-Streamlit-Cloud targets
• Capture a short GIF/MP4 of the dashboard for the README header
• Consider promoting `take_screenshots.py` to a make target or CI artifact step

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