locale:bn was the only locale component with no --locale alias, so the
Bengali docs were reachable through `--with locale:bn` but `--locale bn`
was rejected as an unsupported locale.
Register bn (and the bn-BD alias, matching the ja-JP/zh-CN pattern) in
SUPPORTED_LOCALES and LOCALE_ALIAS_TO_COMPONENT_ID.
The existing test only checked the forward direction — that every alias
resolves to a real component — which is why this gap passed. Add the
reverse assertion: every locale component must be reachable through
--locale.
Co-Authored-By: Kishor Morol <kishormorol@gmail.com>
