Restore device configuration

Push a configuration to the device represented by the given node using the device driver's restore hook (merge semantics over interactive SSH for CLI-driven devices, full override over NETCONF where supported). The configuration comes either from a stored backup, which may belong to a different node (replacement-device scenario), or from the request body. The restore runs as a background task; poll its state with GET /v1/background-tasks/{task-id}. Requires the upload-device-configuration access right on the target node and, when restoring from a backup, the read-device-configuration right on the source node. Every request is recorded in the audit log together with the SHA-256 hash of the configuration; events SYS_DEVICE_CONFIG_RESTORE_STARTED / COMPLETED / FAILED are generated on the target node.