feat(ocr): Add validation system and CLIENT CUI extraction

OCR Data Extraction Validation System:
- Add 7 validation rules (amount range, TVA ratio, payment sum, etc.)
- Add Medium preprocessing to replace Heavy (fixes digit concatenation)
- Add validation warnings to API responses
- Flag receipts needing manual review (needs_manual_review field)
- Add database migration for needs_manual_review column

CLIENT CUI Extraction Improvements:
- Support all format variations: CIF CLIENT:, CLIENT C.U.I/C.I.F., etc.
- Handle OCR errors (R0 vs RO, C1F vs CIF)
- Add client_name, client_cui, client_address to API response
- Add validation fields to API response (was missing)

QA Review: 12 issues found, 9 fixed (5 errors + 4 warnings)
- Fixed type safety in validation rules
- Fixed ZeroDivisionError risk
- Fixed schema mismatch (Optional[bool] for needs_manual_review)
- All 37 unit tests passing

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

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

backend/modules/data_entry/routers/ocr.py

@@ -118,13 +118,23 @@ async def extract_from_image(file: UploadFile = File(...)):
             items_count=result.items_count,
             payment_methods=payment_methods_list,
             suggested_payment_mode=suggested_payment_mode,
+            # Client data (B2B receipts)
+            client_name=result.client_name,
+            client_cui=result.client_cui,
+            client_address=result.client_address,
             confidence_amount=result.confidence_amount,
             confidence_date=result.confidence_date,
             confidence_vendor=result.confidence_vendor,
+            confidence_client=result.confidence_client,
             overall_confidence=result.overall_confidence,
             raw_text=result.raw_text,
             ocr_engine=result.ocr_engine,
             processing_time_ms=result.processing_time_ms,
+            # Validation results
+            needs_manual_review=result.needs_manual_review,
+            validation_warnings=result.validation_warnings,
+            validation_errors=result.validation_errors,
+            inter_ocr_ratios=result.inter_ocr_ratios,
         )
 
         return OCRResponse(success=True, message=message, data=data)
@@ -206,13 +216,23 @@ async def extract_from_attachment(
         items_count=result.items_count,
         payment_methods=payment_methods_list,
         suggested_payment_mode=suggested_payment_mode,
+        # Client data (B2B receipts)
+        client_name=result.client_name,
+        client_cui=result.client_cui,
+        client_address=result.client_address,
         confidence_amount=result.confidence_amount,
         confidence_date=result.confidence_date,
         confidence_vendor=result.confidence_vendor,
+        confidence_client=result.confidence_client,
         overall_confidence=result.overall_confidence,
         raw_text=result.raw_text,
         ocr_engine=result.ocr_engine,
         processing_time_ms=result.processing_time_ms,
+        # Validation results
+        needs_manual_review=result.needs_manual_review,
+        validation_warnings=result.validation_warnings,
+        validation_errors=result.validation_errors,
+        inter_ocr_ratios=result.inter_ocr_ratios,
     )
 
     return OCRResponse(success=True, message=message, data=data)