Fork facesaver -> anime-facesaver: real anime face detector instead of COCO 'person' proxy

Original saved any frame with a big COCO person box (heads, hands,
shoes). Switches to yolov8x6_animeface (HF: Fuyucchi), keeps the
scene-change gate, adds --gpu pinning via CUDA_VISIBLE_DEVICES before
torch init, --download-model, --preview-dir QC mode, optional edge
margin and min face-area fraction.

requirements.txt

@@ -0,0 +1,5 @@
+numpy
+opencv-python
+ultralytics
+scenedetect
+torch