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>