is_auto_update_explicitly_set() -> boolReturn whether an explicit auto-update preference is in force.
True when managed policy decides the value, when
DEEPAGENTS_CODE_AUTO_UPDATE holds a recognized boolean, or when
[update].auto_update is present in config.toml. Distinguishes a
deliberate opt-in/out from the implicit opt-out default.
Managed policy counts: it is the most explicit preference there is, and
omitting it made should_announce_auto_update_default tell the user that
the implicit default was in force on a machine where an administrator had
set the value.