Add pre-built panel detection libraries to vendor directory.
These are copied from node_modules during the build process and
included with the application for panel detection functionality.
Included libraries:
- vendor/opencv/opencv.js - OpenCV.js for image processing
- vendor/tfjs/tf.min.js - TensorFlow.js for ML inference
- vendor/coco-ssd/coco-ssd.min.js - COCO-SSD model for object detection
These files enable the panel mode feature in the reader.
