New --exact-lang CLI flag that enables exact language code matching instead of fuzzy matching. This allows users to get specific regional variants without matching all related variants.
Examples:
- `-l es-419` normally matches all Spanish (es-ES, es-419, es-MX)
- `-l es-419 --exact-lang` matches ONLY es-419 (Latin American Spanish)
Fixes language detection issue where specific variants like es-419 (Latin American Spanish) would match all Spanish variants instead of just close regional variants.
