Allow the next-intl localePrefix mode to be set via environment
variable at build time, defaulting to the existing 'never' behavior.
This is useful when proxying Bulwark under a sub-path (where
'never' can trigger rewrite loops) or when users prefer
URL-embedded locales (/en/settings vs /settings).
Usage:
NEXT_PUBLIC_LOCALE_PREFIX=always npm run build
Accepted values: 'never' (default), 'always', 'as-needed'.
