Step-by-step specification of cc-ci-plan/advisory-scan.py: inputs, the three source
classes and why each is ranked where it is, the union, both classification paths
(patched-version ranges, and the advisory-publish-date fallback for version-scheme
changes), the output contract, and how /recipe-report must read it.
Each rule records the production wrong answer that motivated it — the false 133 from
cross-image counting, the n8n misclassification from reading only vulnerabilities[0],
the '?' sprawl from url punctuation and benign-404s, and the 'never emit 0 for an
undetermined count' rule. Claims cross-checked against the implementation.
Keep this file in the same commit as any behaviour change.
