updateDocument unconditionally set metaDatePrecision/End/Raw from the DTO,
so saving an unrelated edit (a multipart PUT where the form omits the
precision controls) clobbered the stored precision with null — fabricating
a precision the user never chose. Apply each field only when the DTO carries
it, mirroring the existing metadataComplete/scriptType guards.
Refs #666
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>