Adapt factory-reset result parsing to the omnect-os-init JSON contract

[JanZachmann]

omnect-os-init writes the factory-reset result into /run/omnect-device-service/omnect-os-initramfs.json. The current parser in src/twin/factory_reset.rs cannot read that format.

Mismatches

	omnect-os-init writes	ODS expects
JSON key	"factory_reset"	"factory-reset"
status	0..=4 (adds 4 = Warning, see omnect/omnect-os-init#19)	Deserialize_repr enum with 0..=3 only — 4 fails to parse
error	omitted on success (skip_serializing_if)	required String
paths	omitted when empty	required Vec<String>
data_wiped	always present (bool)	not in the struct (ignored by serde, ok)

Effect

• Today: the key lookup omnect_os_initramfs_json["factory-reset"] returns null, so ODS logs "no result" and reports nothing. The reset outcome never reaches the twin. No error is raised.
• After fixing only the key: a result with status: 4 or a missing error/paths makes factory_reset_result() fail. FactoryReset::new()? propagates the error out of Twin::new, so ODS does not start.

Task

Adapt FactoryResetResult/FactoryResetStatus (and the testfiles) to the omnect-os-init contract:

• key factory_reset
• status value 4 (warning: reset succeeded, but a partition needed a second mkfs)
• error, paths, context optional with defaults
• decide how to handle a future unknown status value without failing ODS startup

Contract source: src/runtime/omnect_device_service.rs in omnect/omnect-os-init and its integration tests (tests/factory_reset.rs).