MTConnectObservation.SampleRate was parsed per observation and never read;
MTConnectTagDefinition.MtType/MtSubType/Units were carried (factory blob DTO,
tags[] DTO, probe inference) and only MtCategory was ever read. Deleted. Stored
configs and TagConfig blobs still carrying mtType/mtSubType/units keep loading
(System.Text.Json skips unmapped members) - pinned by a new test. The AdminUI tag
editor reads those keys straight off the blob and is unaffected.
Refs #743
Claude-Session: https://claude.ai/code/session_01Ub9hGmYLQvn9XETzw7CMsT
Joseph Doherty