[codex] Guard country brief i18n namespace (#3911)

* test(country-brief): guard i18n namespace

* test(country-brief): extend i18n guard to all locales

English-only coverage in the previous test would miss any locale that
drops one of the 17 severity/trend/fallback keys. Iterate over every
src/locales/*.json and aggregate missing/empty resolutions into one
failure message so a regression naming "ro.json: countryBrief.fallback.stockIndex"
points straight at the broken locale+key.

* test(country-brief): strip comments before scanning for stale namespace

Addresses greptile P2: assert.doesNotMatch ran on raw file content, so
a future `// was: t('modals.countryBrief.levels.critical')` annotation
would trigger a spurious failure. Route both grep assertions through
stripComments() so only live source is inspected. Synthetic negative
case confirmed: raw text with a commented-out reference matches the
bad pattern, stripped text does not, and the good-pattern match
still passes.