Commits the gzipped 277-deal prod fixture (frozen _price_from_inputs inputs),
the frozen backtest_baseline.json (overall MAPE 18.63% / bias -1.2%; per-segment
бизнес -21.5% / элит -38.6% — the systemic expensive-segment underestimation,
now measured), and a hermetic pytest gate that replays the fixture through the
full pricing spine (ZERO DB) and asserts metrics == baseline within float tolerance.
Relative regression gate, not an absolute SLA (live coverage ~55% is data-blocked
per #1966). To change estimator behaviour: regenerate the baseline
(--from-fixture --update-baseline, no DB) and justify the per-segment deltas in the PR.
The fixture (gzipped prod inputs) re-extracts rarely; the per-change artifact is the
3 KB baseline. Large-file hook excludes the fixture (re-extracted only on ground-truth refresh).
Refs #1966
