Implements camera-based detection system for physical abacus: - VisionCameraFeed: Camera display with Desk View auto-detection - CalibrationOverlay: Interactive quad corner calibration with proper letterbox handling and bounds clamping - Perspective transform using OpenCV.js for rectification - Live rectified preview during calibration - Hooks: useAbacusVision, useDeskViewCamera, useCameraCalibration, useFrameStability 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>