optimize: Reduce Docker image size - remove GUI deps, add aggressive cleanup

fix: Add OpenCV system dependencies for image processing

fix: Multi-strategy OCR for better colored/gradient text extraction

feat: Advanced OCR with image preprocessing for accurate text extraction

Fix: Replace libgl1-mesa-glx with libgl1 for Debian compatibility

v2.0: Add all PDF operations - PDF to Word, Image OCR, PDF Split/Merge