Codex gate (SILENT): panels.js referenced t('cron_model_no_agent_hint') but the key was never added
to i18n.js. t() returns the key name for a missing translation (falls back to LOCALES.en, then the
key), so script-only cron jobs rendered the literal 'cron_model_no_agent_hint'. Added the English key
(other locales fall back to en) + strengthened the i18n-keys test to assert the value is defined.