Adds cv2.QRCodeDetector-based QR reader that subscribes to all four IMX219
CSI camera streams, deduplicates detections with a 2 s per-payload cooldown,
and publishes /saltybot/qr_codes (QRDetectionArray) at 10 Hz. New
QRDetection / QRDetectionArray messages added to saltybot_scene_msgs.
16/16 pure-Python tests pass (no ROS2 required).
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
sl-perception
b2fdc3a500