AssetManager 0.5.5.46

MeshCentral device identity and placeholder serial numbers

Added configurable global serial-number placeholder values.
Added manufacturer-specific placeholder rules using Manufacturer | Serial number.
Placeholder serial numbers are not used for asset matching.
Placeholder serial numbers do not overwrite an existing asset serial number during synchronization.
The MeshCentral node ID remains the stable unique device identity and is used before serial-number matching by default.
The original MeshCentral source value remains available in stored source data when source-data storage is enabled.
Dry-run and live synchronization use the same placeholder detection logic.

The default configuration includes common textual placeholders and a Synology-specific rule for 123456789 and Unknown.