fix: Convert all remaining Date objects to ISO strings and fix client type in factures/nouvelle

app/(main)/factures/impayees/page.tsx

@@ -548,12 +548,12 @@ RECOMMANDATIONS:
                                 <>
                                     <div className="field col-12 md:col-6">
                                         <label htmlFor="datePaiement">Date de paiement</label>
-                                        <Calendar 
-                                            id="datePaiement" 
-                                            value={paymentData.datePaiement} 
-                                            onChange={(e) => setPaymentData(prev => ({ ...prev, datePaiement: e.value || new Date() }))} 
-                                            dateFormat="dd/mm/yy" 
-                                            showIcon 
+                                        <Calendar
+                                            id="datePaiement"
+                                            value={paymentData.datePaiement}
+                                            onChange={(e) => setPaymentData(prev => ({ ...prev, datePaiement: e.value?.toISOString() || new Date().toISOString() }))}
+                                            dateFormat="dd/mm/yy"
+                                            showIcon
                                         />
                                     </div>