Mission: confusion matrix triage — step 6 of 7

Write triage_line(seg): filter the scored rows to the segment, compute the boxes at TH=0.5 plus zero-guarded precision and recall, and print f"{seg:<8} TP={tp} FP={fp} FN={fn} precision={prec:.0%} recall={rec:.0%}". Run it for desktop and mobile — stage 1 of the mission, per-slice matrix plus rates.