Go's encoding/json populates struct fields from case-variant keys like
{"Name":"x"} or {"OwnerId":"y"}, but rest.Put's getFieldNames extracts
raw JSON keys verbatim. With case-sensitive matching, sentFields would
ignore the field on the update side — a request with {"Name":"Renamed"}
would parse into entity.Name but then sent("name") returns false and
the rename silently no-ops.
Normalize both sides to lowercase. The entity-based owner-permission
guard added in the previous commit remains as belt-and-suspenders but
is now redundant with this change.
Also clarify the applyContentUpdate doc comment: namePtr/commentPtr
are nil when the field is absent OR present-but-unchanged, while
publicPtr only tracks presence (an idempotent public is still forwarded).