refactor(auth): extract shared page header into AuthPageHeader component

- add AuthPageHeader component to centralize title/description markup
- replace inline header divs in LoginPage, RegisterPage, LogoutPage, ForgotPasswordPage, ResetPasswordPage, and ConfirmEmailPage with AuthPageHeader

src/features/auth/pages/ResetPasswordPage.client.js

@@ -2,6 +2,7 @@
 
 import { useState } from 'react';
 import { Card, Input, Button, PasswordStrengthIndicator } from '@zen/core/shared/components';
+import AuthPageHeader from '../components/AuthPageHeader.js';
 
 export default function ResetPasswordPage({ onSubmit, onNavigate, email, token }) {
   const [error, setError] = useState('');
@@ -65,14 +66,7 @@ export default function ResetPasswordPage({ onSubmit, onNavigate, email, token }
 
   return (
     <Card variant="default" padding="md" spacing="none" className="w-full max-w-md">
-      <div className="text-center mb-6">
-        <h1 className="text-2xl font-bold text-neutral-900 dark:text-white mb-2">
-          Réinitialiser le mot de passe
-        </h1>
-        <p className="text-sm text-neutral-600 dark:text-neutral-400">
-          Saisissez votre nouveau mot de passe ci-dessous.
-        </p>
-      </div>
+      <AuthPageHeader title="Réinitialiser le mot de passe" description="Saisissez votre nouveau mot de passe ci-dessous." />
 
       {error && !success && (
         <div className="mb-4 p-3 bg-red-50 border border-red-200 rounded-lg dark:bg-red-500/10 dark:border-red-500/20">