Task D — Google-style docstrings (Args/Returns) on every public function,
method, and class across all 158 Python files in the backend. Zero ruff D
violations (pydocstyle Google convention).
Task E — Explanatory one-line comment before every code line (~11600 new
comments). ruff check passes clean after isort re-sort.
- Add UniqueConstraint(test_id, detection_rule_id) named uq_tdr_test_rule to TestDetectionResult model
- Alembic b025: safely deduplicate existing rows before creating constraint