feat(settings): explain that OIDC enables single sign-on

lib/mv_web/live/global_settings_live.ex

@@ -646,6 +646,11 @@ defmodule MvWeb.GlobalSettingsLive do
           </div>
 
           <h3 class="font-medium mb-3">{gettext("OIDC (Single Sign-On)")}</h3>
+          <p data-testid="oidc-sso-description" class="text-sm text-base-content/70 mb-4">
+            {gettext(
+              "OIDC enables Single Sign-On: once configured, members sign in through your identity provider instead of a separate Mila password."
+            )}
+          </p>
           <%= if @oidc_env_configured do %>
             <p class="text-sm text-base-content/70 mb-4">
               {gettext("Some values are set via environment variables. Those fields are read-only.")}