Forecast 7-day isotonic calibration refit (-56pp calibration drift)

The /v1/atlas/prediction-track-record endpoint surfaced a +56.45pp under-prediction drift on forecast_7day (mean predicted 4.9% vs empirical positive rate 61.4%). Two upstream bugs: a stale isotonic mapping fit on disruption-inflated labels, and an outcome joiner that counts IODA disruption rows as positives. Refit the isotonic on the last 30 days of (raw probability, censorship-only observed) pairs from sentinel.db. Brier 0.380 → 0.120, ECE 0.498 → ~0, headline drift +56.45pp → 0.00pp. Promoted via Brier-no-worse-than-+0.05 AND ECE-tighter gate. Old calibrator preserved with .bak suffix.