fix(normalizer): defang leading LF in CSV + assert pinned workbook timestamp

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

tools/import-normalizer/tests/test_writers.py

@@ -31,6 +31,14 @@ def test_write_documents_xlsx_joins_lists(tmp_path):
     assert row["receiver_person_ids"] == "a|b"
     assert row["needs_review"] == "unparsed_date"
 
+def test_write_documents_xlsx_pins_timestamp(tmp_path):
+    # determinism (NFR-IDEM-01): workbook created/modified are pinned, not the current time
+    doc = documents.CanonicalDocument(index="W-0001")
+    out = tmp_path / "d.xlsx"
+    writers.write_documents_xlsx([doc], out)
+    wb = openpyxl.load_workbook(out)
+    assert (wb.properties.created.year, wb.properties.created.month, wb.properties.created.day) == (2020, 1, 1)
+
 def test_write_review_csv(tmp_path):
     out = tmp_path / "r.csv"
     writers.write_review_csv(out, ["raw", "count"], [["?", 3], ["x", 1]])