feat: give payment its own page

The PIX and card choices appeared under the cart, on the same page as the
customer's details. "Ir para o pagamento" now sends the order and opens
/pagamento, step 3 of the progress bar: the server's order summary, then PIX
or card, each opening below. The cart keeps only the sending progress and its
errors; a changed cart is sent again instead of offering the old quote.
Portal links open the payment page.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

web/portal.js

@@ -18,7 +18,7 @@ async function load(){
     for(const quote of data.quotes){
       const card=node('article');card.className='card';card.append(node('h3','Cotação '+quote.id.slice(0,8)));
       card.append(node('p',quote.approved?'Total aprovado: '+money(quote.approved.total_cents):'Aguardando conferência de metragem e nota.'));
-      const link=node('a','Abrir cotação no Site');link.href='/carrinho?quote='+quote.id;card.append(link);$('quotes').append(card);
+      const link=node('a','Abrir cotação no Site');link.href='/pagamento?quote='+quote.id;card.append(link);$('quotes').append(card);
     }
     $('orders').replaceChildren();
     if(!data.orders.length)$('orders').append(node('p','Nenhum pedido pago nesta conta ou sessão.'));