HEL-282: 写库路径事务提交与审计留痕自查修复

同类未提交即 close 回滚、业务与审计拆成两笔事务的路径一并收进可嵌套事务边界。

Co-authored-by: Cursor <cursoragent@cursor.com>
Co-authored-by: multica-agent <github@multica.ai>

src/bank_importer/auth.py

@@ -18,7 +18,7 @@ import secrets
 import sqlite3
 import string
 
-from .db import utc_now
+from .db import transaction, utc_now
 
 
 MIN_PASSWORD_LENGTH = 8
@@ -308,7 +308,7 @@ def audit(
     ip: str | None = None,
 ) -> None:
     """Append an audit log entry. Never pass passwords in ``detail``."""
-    with connection:
+    with transaction(connection):
         connection.execute(
             """
             INSERT INTO audit_log (