Add Catalan (ca) language support

None of the bundled engines (Qwen3-TTS, Kokoro, Chatterbox Multilingual) currently support Catalan (`ca`), a language spoken by ~10 million people and co-official in Catalonia, the Balearic Islands, Valencia, and Andorra. There's already an open upstream request for this on Chatterbox: resemble-ai/chatterbox#517, which links to existing open Catalan TTS resources from Projecte AINA (BSC-CNS): a published multi-accent model (matxa-tts-cat-multiaccent) and training/eval datasets (LaFresCat, commonvoice_benchmark_catalan_accents). Flagging here too so it's on Voicebox's radar once upstream support lands, or in case another bundled engine could pick it up sooner. Happy to help test.