Adds a step-through tool for creating 100% correct reference data (ground truth) with position information. Users scan a page, review each vocabulary entry with image crops, confirm or correct the OCR text, and save the result as JSON. Backend: extract_entries_with_boxes() helper + 3 endpoints (extract-with-boxes, ground-truth save/load). Frontend: GroundTruthPanel component with SVG overlay, ImageCrop, keyboard shortcuts (Enter/Tab/arrows), and tab navigation in page.tsx. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>