FaceDetectorYN was created with a hardcoded score_threshold of 0.5, so
configured face_recognition.detection_threshold values below 0.5 had no
effect: lower-confidence faces were discarded inside OpenCV before the
config threshold was applied as a post-filter.
On cameras with low-resolution detect streams (e.g. 736x416 substreams),
real faces routinely score 0.3-0.5 in YuNet, so face recognition never
ran on them even though the embedding model handles such crops well.
Cap the internal threshold at the configured value instead.
