- install.sh: default username/password to admin on fresh install
- user.go: UpdateFirstUser resets Role to admin, preventing lockout
- user.html: show remaining traffic and last online time
- i18n: remove 11 translation files, keep only en_US and zh_CN
- LanguageManager: trim supportedLanguages to 2 entries, remove simularLangs
Add a simplified dashboard page for non-admin users showing username,
traffic usage, expiry time, and logout button. Implement role-based
routing so user-role accounts are redirected to their own dashboard
instead of the admin panel. Add getUserInfo API endpoint and i18n
translations across all 13 supported locales.