Pre-assign devices to locations

Pre-assign device serial numbers to locations, identified by Location ID or nodeId, so each device pairs automatically into its assigned location the first time it is plugged in. Submit up to 1000 rows in one request; all rows are validated before any are saved. Re-uploading the same rows is safe and does not create duplicates, and dryRun validates rows without saving them. A serial number already assigned to another workspace is refused with a conflict error, and the action is recorded in the activity log.