fix: logging KeyError with reserved 'filename' key, pytest return-not-none warnings

- api_server.py: rename 'filename' to 'file_name' in upload_file log extra
  dict to avoid collision with Python logging's reserved LogRecord attribute
- test_e2e_ocr.py: replace return statements with assert in test functions
  to fix PytestReturnNotNoneWarning

tests/test_e2e_ocr.py

@@ -85,7 +85,8 @@ def test_ocr_extraction_pipeline():
         print(f"  值: {fields[0].get('field_value', 'N/A')}")
         print(f"  坐标: {fields[0].get('bbox', 'N/A')}")
 
-    return all_ok
+    # OCR field extraction is informational; verify we got a valid response
+    assert extraction.get("ocr_available") is not None
 
 
 def test_validation_service():
@@ -94,7 +95,7 @@ def test_validation_service():
     result = validate_jrxml("<jasperReport/>")
     print(f"  状态: {'OK' if result else 'FAIL'}")
     print(f"  响应: {result}")
-    return True
+    assert result is not None
 
 
 def test_ocr_fallback():