feat(auth): implement auto guest mode and enhance token system

- Add role-based token system with metadata support
- Implement automatic guest mode for unconfigured authentication
- Create new /auth-status endpoint for authentication status checking
- Modify frontend to auto-detect auth status and bypass login when appropriate
- Add guest mode indicator in site header for better UX

This change allows users to automatically access the system without manual
login when authentication is not configured, while maintaining secure
authentication when credentials are properly set up.

lightrag_webui/src/features/SiteHeader.tsx

@@ -57,7 +57,7 @@ function TabsNavigation() {
 export default function SiteHeader() {
   const { t } = useTranslation()
   const navigate = useNavigate()
-  const { logout } = useAuthStore()
+  const { logout, isGuestMode } = useAuthStore()
 
   const handleLogout = () => {
     logout()
@@ -74,6 +74,11 @@ export default function SiteHeader() {
 
       <div className="flex h-10 flex-1 justify-center">
         <TabsNavigation />
+        {isGuestMode && (
+          <div className="ml-2 self-center px-2 py-1 text-xs bg-amber-100 text-amber-800 dark:bg-amber-900 dark:text-amber-200 rounded-md">
+            {t('login.guestMode', 'Guest Mode')}
+          </div>
+        )}
       </div>
 
       <nav className="flex items-center">