feat: add receipt OCR pipeline (refs #69)

Implement receipt-specific OCR extraction for fuel receipts:

- Pattern matching modules for date, currency, and fuel data extraction
- Receipt-optimized image preprocessing for thermal receipts
- POST /extract/receipt endpoint with field extraction
- Confidence scoring per extracted field
- Cross-validation of fuel receipt data
- Unit tests for all pattern matchers

Extracted fields: merchantName, transactionDate, totalAmount,
fuelQuantity, pricePerUnit, fuelGrade

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

ocr/app/models/__init__.py

@@ -7,6 +7,8 @@ from .schemas import (
     JobStatus,
     JobSubmitRequest,
     OcrResponse,
+    ReceiptExtractedField,
+    ReceiptExtractionResponse,
     VinAlternative,
     VinExtractionResponse,
 )
@@ -19,6 +21,8 @@ __all__ = [
     "JobStatus",
     "JobSubmitRequest",
     "OcrResponse",
+    "ReceiptExtractedField",
+    "ReceiptExtractionResponse",
     "VinAlternative",
     "VinExtractionResponse",
 ]