feat(setup): center onboarding and add secure token help

frontend/app/setup/page.tsx

@@ -4,6 +4,7 @@ import { useEffect, useState, type FormEvent } from "react";
 import { apiUrl, requestJson } from "../lib/api-client";
 import { authFetch, ForbiddenError, logout, setToken, UnauthorizedError } from "../lib/auth";
 import MagentMark from "../ui/MagentMark";
+import SetupTokenHelp from "./SetupTokenHelp";
 import { serviceStatusLabel } from "../admin/configNavigation";
 import {
   ALL_FIELDS,
@@ -352,7 +353,7 @@ export default function SetupPage() {
               Retry
             </button>
           ) : forbidden ? (
-            <section className={styles.panel}>
+            <section className={`${styles.panel} ${styles.accountPanel}`}>
               <h2>Administrator access required</h2>
               <p>Ask an administrator to finish installation.</p>
               <button type="button" disabled={!!busy} onClick={switchAccount}>
@@ -360,19 +361,12 @@ export default function SetupPage() {
               </button>
             </section>
           ) : !admin ? (
-            <section className={styles.panel}>
+            <section className={`${styles.panel} ${styles.accountPanel}`}>
               <h2>{status.needs_admin ? "Create your administrator" : "Sign in to continue"}</h2>
               <p>
-                {status.needs_admin ? (
-                  <>
-                    Enter the SETUP_TOKEN from your deployment environment. For a managed Portainer install, open the
-                    Magent container console and run <code>python -m app.container_bootstrap setup-token</code> to
-                    retrieve it. Only the server operator can create the first administrator; the console command stops
-                    returning the token after that account exists.
-                  </>
-                ) : (
-                  "Use your local Magent administrator account. Settings are never available to unauthenticated visitors."
-                )}
+                {status.needs_admin
+                  ? "Use your private setup token to create the first administrator account."
+                  : "Use your local Magent administrator account. Settings are never available to unauthenticated visitors."}
               </p>
               <form onSubmit={authenticate} className={styles.account}>
                 {status.needs_admin && (
@@ -409,8 +403,11 @@ export default function SetupPage() {
                       maxLength={1024}
                       value={setupToken}
                       onChange={(event) => setSetupToken(event.target.value)}
+                      aria-describedby="setup-token-hint"
                       disabled={!!busy}
                     />
+                    <p id="setup-token-hint">Retrieve this token from your server console.</p>
+                    <SetupTokenHelp disabled={!!busy} />
                   </div>
                 )}
                 <div className={styles.field}>