[IDEA] Add Portuguese (pt-BR)

这个功能请求是用来解决什么问题的？ / Is your feature request related to a problem? Please describe. I'm always frustrated when I try to use the application in Portuguese, but the default language configurations and the web UI do not natively list Brazilian Portuguese (pt-BR) as an option. This makes it slightly difficult for Portuguese speakers to interact with the VTuber out of the box without diving into the source code to modify configurations and translate the frontend UI.

您期望的解决方案是什么？ / Describe the solution you'd like I'd like to add full support for Brazilian Portuguese (pt-BR) to both the backend and frontend:

Frontend (Open-LLM-VTuber-Web): Add a pt-BR/translation.json file containing all the UI translations, register it in i18n.ts, and add it to the languages dropdown menu in the General Settings (general.tsx). Backend (Open-LLM-VTuber): Add pt-BR to the default supported languages list for ASR configurations (like Azure ASR and generic configs) in asr.py, asr_factory.py, and the conf.default.yaml templates. 此功能为何对 Open-LLM-VTuber 很重要？ / Why is this important for Open-LLM-VTuber? This feature is very important because it expands accessibility for a huge community of Portuguese speakers (mainly from Brazil). By natively supporting pt-BR, we lower the entry barrier for new users in this demographic, improving user experience and making the AI VTuber feel much more personal and welcoming.

您考虑过哪些替代方案？ / Describe alternatives you've considered An alternative would be leaving it as it is, requiring users to manually edit their own conf.yaml for ASR fallback languages and individually customizing and building the frontend to get translations, which is a big hassle for regular users who just want to use the application.

您是否愿意参与开发此功能？ / Would you like to work on this issue? Yes! I have already implemented and tested these changes locally and can submit a Pull Request right away.

补充信息 / Additional context No extra context needed. The changes are straightforward and do not alter the core architecture of the project.