* feat(i18n): enhance language management by saving user preference and detecting browser language
- Added a watcher to save the selected language to localStorage on change.
- Implemented browser language detection to set the default language based on user settings or browser preferences.
* use ~/utils/localstorage, remove setting savedLang in mounted as this is already set in i18.ts.
* do not repeat fallbackLocale and remove console log.
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Co-authored-by: Miroslav Šedivý <sedivy.miro@gmail.com>