FIXES:
- OCR now uses lazy initialization (only loads when first used)
- Fixed PaddleOCR invalid use_gpu parameter (some versions don't support it)
- Added fallback try/except for PaddleOCR without use_gpu
- App starts immediately, OCR initializes on first scan
- Prevents long startup delays from model downloading
CHANGES:
- OCRService._init_backends() only called on first use
- Removed eager initialization from main.py startup
- Better error handling for backend failures
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