fix: 遗留清理（枚举同源/边界防御/断言补强）

tests/test_free_text_extractor.py

@@ -1,4 +1,4 @@
-from genesis.data_models import CellValue, ExcelTable, SheetType
+from genesis.data_models import CellValue, ExcelTable, ExtractionMethod, SheetType
 from genesis.parsers.free_text_extractor import build_free_text_table, extract_text_blocks
 
 
@@ -15,3 +15,8 @@ def test_build_free_text_table():
     assert len(table.rows) == 2
     assert isinstance(table.rows[0]["text"], CellValue)
     assert table.rows[0]["text"].value == "A"
+
+
+def test_free_text_uses_enum_value():
+    table = build_free_text_table("メモ", ["A"], "f.xlsx")
+    assert table.extraction_method == ExtractionMethod.LLM_FROM_FREE_TEXT.value