Live 30-day production track record across all forecast models

New endpoint /v1/atlas/prediction-track-record joins daily-logged forecasts against observed incidents. forecast_7day (v1) ships with empirical precision 0.69 / recall 0.39 over the last 720 predictions; the other 11 models surface training-time metrics with n_predictions=0 + an honest caveat until per-request prod logging lands.