Add desktop GUI language switching

[0xtootoo29]

Summary

• add a desktop i18n catalog with English and Simplified Chinese strings
• add a language selector in Appearance settings and persist it to Hermes display.language
• wire common desktop navigation, chat/sidebar actions, settings, boot failure, and install progress copy to the selected language

Verification

• npm run type-check
• npx eslint src/i18n.ts src/app/chat/composer/index.tsx src/app/settings/config-settings.tsx
• npm run build
• local preview returned HTTP 200 and built assets contain the Chinese GUI strings

Note: full desktop lint still reports existing unrelated errors in other files.

[teknium1]

Superseded by #38241, which we merged as the desktop i18n foundation + Simplified Chinese translation. It aligns with our existing web/src/i18n pattern (typed Translations, I18nProvider/useI18n, display.language config key), was already green across CI, and merged cleanly. Thanks for the work on localization — this is exactly the direction we wanted, and your effort helped confirm it. #38241