feat(front): ajouter champ promoCode pour commandes

my-library/src/pages/Orders.jsx

@@ -6,6 +6,7 @@ export default function Orders() {
   const [paymentMethod, setPaymentMethod] = useState('CREDIT_CARD');
   const [address, setAddress] = useState({ street: '', city: '', postalCode: '', country: '' });
   const [lines, setLines] = useState([{ bookId: '', quantity: 1 }]);
+  const [promoCode, setPromoCode] = useState('');
   const [message, setMessage] = useState(null);
   const [submitting, setSubmitting] = useState(false);
 
@@ -37,6 +38,7 @@ export default function Orders() {
         bookId: Number(line.bookId),
         quantity: Number(line.quantity),
       })),
+      ...(promoCode ? { promoCode } : {}),
     };
 
     createOrder(payload)
@@ -77,6 +79,9 @@ export default function Orders() {
         <input name="country" placeholder="Pays" value={address.country} onChange={handleAddressChange} required />
 
         <h2>Paiement</h2>
+        <label>Code promo
+          <input value={promoCode} onChange={(e) => setPromoCode(e.target.value)} placeholder="Code promo (optionnel)" />
+        </label>
         <select value={paymentMethod} onChange={(e) => setPaymentMethod(e.target.value)}>
           <option value="CREDIT_CARD">Carte bancaire</option>
         </select>