fix(transfers): warn when owner key mapper is missing

Logs the expected path on FileNotFoundError to make missing mappings visible and easier to diagnose.

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: ksmuczynski

transfers/contact_transfer.py

@@ -62,6 +62,10 @@ def __init__(self, *args, **kw):
             with open(ownerkey_mapper_path, "r") as f:
                 self._ownerkey_mapper = json.load(f)
         except FileNotFoundError:
+            logger.warning(
+                "Owner key mapper file not found at '%s'; proceeding with empty owner key mapping.",
+                ownerkey_mapper_path,
+            )
             self._ownerkey_mapper = {}
 
         self._added = []