refactor(sp41): align submission_dedup with cyclone.store conventions (main Base, db.SessionLocal, now(timezone.utc), exceptions.py)

backend/tests/test_submission_dedup.py

@@ -1,7 +1,7 @@
 """Claim-id dedup at the SFTP pre-flight stage."""
 from datetime import datetime
+from cyclone.store.exceptions import DuplicateClaimError
 from cyclone.store.submission_dedup import (
-    DuplicateClaimError,
     record_submission,
     check_duplicate,
     DEFAULT_WINDOW_DAYS,
@@ -35,4 +35,4 @@ def test_check_duplicate_passes_after_window(tmp_path):
 
 
 def test_default_window_is_30_days():
-    assert DEFAULT_WINDOW_DAYS == 30
+    assert DEFAULT_WINDOW_DAYS == 30