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/tests/test_date_patterns.py

@@ -0,0 +1,163 @@
+"""Tests for date pattern matching."""
+import pytest
+
+from app.patterns.date_patterns import DatePatternMatcher, date_matcher
+
+
+class TestDatePatternMatcher:
+    """Test date pattern extraction."""
+
+    def test_mm_dd_yyyy_slash(self) -> None:
+        """Test MM/DD/YYYY format."""
+        text = "DATE: 01/15/2024"
+        result = date_matcher.extract_best_date(text)
+
+        assert result is not None
+        assert result.value == "2024-01-15"
+        assert result.confidence > 0.9
+
+    def test_mm_dd_yy_slash(self) -> None:
+        """Test MM/DD/YY format with 2-digit year."""
+        text = "01/15/24"
+        result = date_matcher.extract_best_date(text)
+
+        assert result is not None
+        assert result.value == "2024-01-15"
+
+    def test_mm_dd_yyyy_dash(self) -> None:
+        """Test MM-DD-YYYY format."""
+        text = "01-15-2024"
+        result = date_matcher.extract_best_date(text)
+
+        assert result is not None
+        assert result.value == "2024-01-15"
+
+    def test_iso_format(self) -> None:
+        """Test ISO YYYY-MM-DD format."""
+        text = "2024-01-15"
+        result = date_matcher.extract_best_date(text)
+
+        assert result is not None
+        assert result.value == "2024-01-15"
+        assert result.confidence > 0.95
+
+    def test_month_name_format(self) -> None:
+        """Test 'Jan 15, 2024' format."""
+        text = "Jan 15, 2024"
+        result = date_matcher.extract_best_date(text)
+
+        assert result is not None
+        assert result.value == "2024-01-15"
+
+    def test_month_name_no_comma(self) -> None:
+        """Test 'Jan 15 2024' format without comma."""
+        text = "Jan 15 2024"
+        result = date_matcher.extract_best_date(text)
+
+        assert result is not None
+        assert result.value == "2024-01-15"
+
+    def test_day_month_year_format(self) -> None:
+        """Test '15 Jan 2024' format."""
+        text = "15 Jan 2024"
+        result = date_matcher.extract_best_date(text)
+
+        assert result is not None
+        assert result.value == "2024-01-15"
+
+    def test_full_month_name(self) -> None:
+        """Test full month name like 'January'."""
+        text = "January 15, 2024"
+        result = date_matcher.extract_best_date(text)
+
+        assert result is not None
+        assert result.value == "2024-01-15"
+
+    def test_multiple_dates_returns_best(self) -> None:
+        """Test that multiple dates returns highest confidence."""
+        text = "Date: 01/15/2024\nExpires: 01/15/2025"
+        results = date_matcher.extract_dates(text)
+
+        assert len(results) == 2
+        # Both should be valid
+        assert all(r.confidence > 0.5 for r in results)
+
+    def test_invalid_date_rejected(self) -> None:
+        """Test that invalid dates are rejected."""
+        text = "13/45/2024"  # Invalid month/day
+        result = date_matcher.extract_best_date(text)
+
+        assert result is None
+
+    def test_receipt_context_text(self) -> None:
+        """Test date extraction from realistic receipt text."""
+        text = """
+        SHELL STATION
+        123 MAIN ST
+        DATE: 01/15/2024
+        TIME: 14:32
+        PUMP #5
+        REGULAR 87
+        10.500 GAL
+        TOTAL $38.50
+        """
+        result = date_matcher.extract_best_date(text)
+
+        assert result is not None
+        assert result.value == "2024-01-15"
+
+    def test_no_date_returns_none(self) -> None:
+        """Test that text without dates returns None."""
+        text = "SHELL STATION\nTOTAL $38.50"
+        result = date_matcher.extract_best_date(text)
+
+        assert result is None
+
+    def test_confidence_boost_near_keyword(self) -> None:
+        """Test confidence boost when date is near DATE keyword."""
+        text_with_keyword = "DATE: 01/15/2024"
+        text_without = "01/15/2024"
+
+        result_with = date_matcher.extract_best_date(text_with_keyword)
+        result_without = date_matcher.extract_best_date(text_without)
+
+        assert result_with is not None
+        assert result_without is not None
+        # Keyword proximity should boost confidence
+        assert result_with.confidence >= result_without.confidence
+
+
+class TestEdgeCases:
+    """Test edge cases in date parsing."""
+
+    def test_year_2000(self) -> None:
+        """Test 2-digit year 00 is parsed as 2000."""
+        text = "01/15/00"
+        result = date_matcher.extract_best_date(text)
+
+        assert result is not None
+        assert result.value == "2000-01-15"
+
+    def test_leap_year_date(self) -> None:
+        """Test Feb 29 on leap year."""
+        text = "02/29/2024"  # 2024 is a leap year
+        result = date_matcher.extract_best_date(text)
+
+        assert result is not None
+        assert result.value == "2024-02-29"
+
+    def test_leap_year_invalid(self) -> None:
+        """Test Feb 29 on non-leap year is rejected."""
+        text = "02/29/2023"  # 2023 is not a leap year
+        result = date_matcher.extract_best_date(text)
+
+        assert result is None
+
+    def test_september_abbrev(self) -> None:
+        """Test September abbreviation (Sept vs Sep)."""
+        for abbrev in ["Sep", "Sept", "September"]:
+            text = f"{abbrev} 15, 2024"
+            result = date_matcher.extract_best_date(text)
+
+            assert result is not None, f"Failed for {abbrev}"
+            assert result.value == "2024-09-15"