Models now declare $hidden for passwords, tokens, db URLs, and compose
fields. API controllers flip from makeHidden-on-deny to makeVisible-on-
allow (can_read_sensitive=true), fixing fields that were never hidden.
Also adds missing fields (mysql/mariadb passwords, logdrain keys, etc.)
to privileged disclosure lists.
Tests added: Feature/Security/ApiSensitiveFieldsTest and
Unit/Models/SensitiveFieldsHiddenTest cover all affected models and
controllers.
