CI/CD Basics (Lint + Test + Build)

# CI/CD Basics (Lint + Test + Build, Branch Protections) Extend the `.github/workflows/ci.yml` pattern with a build gate: lint, unit tests, Docker build, and smoke — all green before merge. ## 1. Pipeline stages Lint (ruff/flake8) -> unit tests (`pytest -q`) -> `docker build` -> containerized smoke (`test_smoke.py`). Fail fast in that order: cheap checks first. ## 2. Branch protections `main` requires the CI workflow green + 1 review. No direct pushes; model promotion happens via PR with the run-comparison report attached. ## 3. Build gate vs deploy gate CI build gate (this lesson) proves the artifact is sound. The deploy gate (m5 flagship) proves the artifact runs somewhere real with a live URL.