feat(core): implement extractor, pdf_parser, and utils with TDD

Wave 2 tasks complete:
- Task 4: ZUGFeRD extractor with profile detection (factur-x)
- Task 5: PDF text parser with regex patterns
- Task 6: Utils with unit code mapping and tolerance checks

Features:
- extract_zugferd() extracts XML and text from PDFs
- parse_zugferd_xml() parses UN/CEFACT CII XML to models
- extract_from_text() extracts values using regex patterns
- translate_unit_code() maps UN/ECE codes to German
- amounts_match() checks with 0.01 EUR tolerance
- German number/date format handling

Tests: 27 utils tests, 27 pdf_parser tests, extractor tests

.sisyphus/plans/zugferd-service.md

@@ -515,7 +515,7 @@ Critical Path: Task 1 → Task 4 → Task 7 → Task 10 → Task 13 → Task 16
 
 ### Wave 2: Core Extraction Logic
 
-- [ ] 4. ZUGFeRD Extractor Implementation (TDD)
+- [x] 4. ZUGFeRD Extractor Implementation (TDD)
 
   **What to do**:
   - Write tests first using sample PDFs from fixtures
@@ -636,7 +636,7 @@ Critical Path: Task 1 → Task 4 → Task 7 → Task 10 → Task 13 → Task 16
 
 ---
 
-- [ ] 5. PDF Text Parser Implementation (TDD)
+- [x] 5. PDF Text Parser Implementation (TDD)
 
   **What to do**:
   - Write tests first with expected extraction patterns
@@ -738,7 +738,7 @@ Critical Path: Task 1 → Task 4 → Task 7 → Task 10 → Task 13 → Task 16
 
 ---
 
-- [ ] 6. Utility Functions Implementation
+- [x] 6. Utility Functions Implementation
 
   **What to do**:
   - Create UN/ECE unit code mapping dictionary