Fix the autocorrelation threshold at a 5% false alarm rate

Fix the autocorrelation threshold at a 5% false alarm rate

Compute the lag-1 autocorrelation trend statistic on a separate development set only, then set the threshold that yields a 5% false alarm rate on drifting-noise series. Freeze the statistic and the threshold before touching the 1,000-series test set. Deliverable: A frozen configuration with the statistic definition, the window length, the threshold, and the development-set false alarm curve.