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/site-steps.js

@@ -11,6 +11,7 @@ const TITULO_INICIO=document.title;
 function tituloPagina(){
   const p=paginaDe(location.pathname);
   if(p.pagina==='carrinho') return 'Carrinho · DTF Dropstar';
+  if(p.pagina==='pagamento') return 'Pagamento · DTF Dropstar';
   if(p.pagina==='produto') return MODOS[p.modo].tit+' · DTF Dropstar';
   return TITULO_INICIO;
 }
@@ -91,7 +92,7 @@ function vaiPara(url){
     passos.hidden = r==='inicio' || carrinhoVazio;
     alturas();
     if(!passos.hidden){
-      const atual = r==='produto' ? 1 : temCheckout() ? 3 : 2;
+      const atual = r==='produto' ? 1 : r==='pagamento' ? 3 : 2;
       passos.querySelectorAll('[data-passo]').forEach(a=>{
         const n=Number(a.dataset.passo);
         a.classList.toggle('atual',n===atual); a.classList.toggle('feito',n<atual);
@@ -124,8 +125,10 @@ function vaiPara(url){
 
   // Payment is a step only once the order has been sent.
   passos.querySelector('[data-passo="3"]').addEventListener('click',e=>{
-    if(!temCheckout()) e.preventDefault();
-  });
+    let enviado=false;
+    try{ enviado=!!localStorage.getItem('dtf-quote'); }catch(_){}
+    if(!enviado){ e.preventDefault(); e.stopPropagation(); }
+  },true);
   $('barraMBtn').addEventListener('click',e=>{
     e.preventDefault();
     alvoBarra()?.scrollIntoView({behavior:'smooth',block:'center'});