Fix model extraction path for buffalo_sc v0.7 zip

The InsightFace buffalo_sc.zip release changed its internal layout —
files are now at the zip root (w600k_mbf.onnx) rather than under a
buffalo_sc/ subdirectory. The mismatched path caused a KeyError on
first run, crashing the app with exit code 1.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

recognizer/face_db.py

@@ -29,7 +29,7 @@ MODEL_URL  = (
     "https://github.com/deepinsight/insightface"
     "/releases/download/v0.7/buffalo_sc.zip"
 )
-_REC_ENTRY = "buffalo_sc/w600k_mbf.onnx"   # path inside the zip
+_REC_ENTRY = "w600k_mbf.onnx"   # path inside the zip (root-level since buffalo_sc v0.7)
 
 _CASCADE = cv2.CascadeClassifier(
     cv2.data.haarcascades + "haarcascade_frontalface_default.xml"