No coverage reporting wired into CI

[joelsansana]

CI runs pytest (smoke + full suite) across Python 3.10–3.12 and ruff check, but there's no pytest-cov/coverage step. This means real gaps — like fouling-mode windows having no batch-path test because there's no batch-path code (issue #4) — aren't visible without manually grepping test files.

Suggested fix: add pytest-cov as a test dependency and a coverage step/report in ci.yml, optionally with a minimum-coverage gate.

Files: .github/workflows/ci.yml, pyproject.toml

[joelsansana]

Fixed in 75d4212. Added pytest-cov as a test dependency and a coverage step in ci.yml that runs the full suite under coverage, prints the term-missing report, and uploads coverage.xml as a workflow artifact (30-day retention, even on failure). No minimum-coverage gate — coverage is informational; the dashboard's bdsim import path is exercised in dashboard-side tests, not here.