udp/config: fall back to default_owner when os_info has no owner; log debug

- When os_info arrives with no owner field, apply default_owner from server config
- Stop applying default_owner unconditionally in get_host_access (now deferred to os_info handling)
- os_info plugin logs debug message when injecting owner from client config

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

hbd/client/plugins/os_info.py

@@ -63,6 +63,7 @@ class OSInfoPlugin(InfoPlugin):
                 "hbc_type": "full",
             }
             if self.config.get("owner"):
+                self.logger.debug(f"Adding owner from config: {self.config['owner']}")
                 data["owner"] = self.config["owner"]
             
             # Add Linux-specific distribution info