Fix: auto-detect device for GPU/CPU fallback

Use torch.cuda.is_available() to auto-detect device.
Falls back to CPU when GPU is not available.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

app.py

@@ -29,10 +29,13 @@ def detect(image, face_score_threshold, landmark_score_threshold):
     """Detect anime faces and landmarks in the image."""
     global detector
 
-    # Lazy initialization on GPU
+    # Lazy initialization with auto device detection
     if detector is None:
         from anime_face_detector import create_detector
-        detector = create_detector('yolov3', device='cuda:0')
+        # Auto-detect device: use GPU if available, otherwise CPU
+        device = 'cuda:0' if torch.cuda.is_available() else 'cpu'
+        print(f'Using device: {device}')
+        detector = create_detector('yolov3', device=device)
 
     # Convert RGB to BGR for OpenCV
     image_bgr = cv2.cvtColor(image, cv2.COLOR_RGB2BGR)