- Language enum: en-US, en-GB, es, fr, hi, it, ja, pt-BR, zh
- Engine-specific mappings (kokoro → single-letter) live in pipeline_factory and synthesize
- spacy_utils uses Language enum keys for model mapping
- split_pattern uses Language enum properties (is_cjk)
- Updated all tests to use ISO codes
- SubtitleMode, OutputFormat, SaveMode, SubtitleFormat, InputFormat
- Properties: dot_ext, is_lossless, is_book, is_subtitle
- from_str/from_path class methods with normalization
- Updated domain and application layers to use Enums
- 17 new tests for enum validation and properties