Replace the language cycling button on the login page with a dropdown
showing all 14 supported languages. Add automatic browser/OS language
detection via navigator.languages, falling back to a configurable
DEFAULT_LANGUAGE env var, then 'en' as last resort.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Add Arabic to the client i18n system, expose it in the language selectors, and enable RTL document handling. Also localize the remaining language-specific UI bits used by the login, demo, Vacay, and GitHub panels.