Implement OCR language-pack management infrastructure resolving OQ-04.
Components implemented:
- detect_available_languages() - scans tessdata for .traineddata files
- validate_ocr_languages() - validates requested languages, emits diagnostics
- ExtractionOptions.ocr_language field with default vec!["eng"]
- OCR_LANGUAGE_UNAVAILABLE diagnostic code
- Doctor check for language verification
- docs/notes/ocr-language-packs.md with distribution strategy
OQ-04 Resolution: Bundled in Docker images with tiered strategy
- pdftract:ocr (~150 MB) - eng + 13 common languages
- pdftract:full (~600 MB) - All 100+ languages
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
