✨(frontend) support 'silent' and 'returnTo' params in authUrl

Enhanced the authentication URL generation to support 'silent'
and 'returnTo' query parameters.

This allows initiating a silent login and specifying a custom
return URL after auth.

src/frontend/src/features/auth/utils/authUrl.ts

@@ -1,5 +1,5 @@
 import { apiUrl } from '@/api/apiUrl'
 
-export const authUrl = () => {
-  return apiUrl('/authenticate')
+export const authUrl = (silent = false, returnTo = window.location.href) => {
+  return apiUrl(`/authenticate?silent=${encodeURIComponent(silent)}&returnTo=${encodeURIComponent(returnTo)}`)
 }