feat: Add OCR integration for automatic receipt data extraction

Implement Tesseract-based OCR to automatically extract vendor name,
date, total amount, and VAT from uploaded receipt images/PDFs,
reducing manual data entry and improving accuracy.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

data-entry-app/backend/requirements.txt

@@ -30,3 +30,11 @@ httpx>=0.26.0
 # Testing
 pytest>=8.0.0
 pytest-asyncio>=0.23.3
+
+# OCR Dependencies
+paddleocr>=2.7.0
+paddlepaddle>=2.5.0
+opencv-python>=4.8.0
+pytesseract>=0.3.10
+pdf2image>=1.16.0
+numpy>=1.24.0