Standardize the dashboard role VALUE on the canonical six: Admin→Administrator
(Viewer unchanged). Pure value rename via DashboardRoles.Admin constant +
appsettings GroupToRole; the GatewayOptionsValidator allowed-set/message track
the constant so they now require 'Administrator' or 'Viewer'. Enforcement is
unchanged — Administrator authorizes exactly what Admin did.
Dashboard roles are derived at login from LDAP groups via GroupToRole and are
never persisted to the SQLite auth store, so no DB migration/seed change.
UNTOUCHED: the separate gRPC API-key scope GatewayScopes.Admin = "admin"
(lowercase) and every "admin" scope literal — a distinct data-plane system.