Word-lookup from full-page Tesseract is fast but can miss small or isolated words (e.g. "Ei"). Now falls back to per-cell Tesseract OCR for cells that remain empty after word-lookup. The ocr_engine field reports 'cell_ocr_fallback' for cells that needed the fallback. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>