feat: choose which cart items to pay, with a thumbnail of each

Each cart item has a checkbox and a thumbnail of its first file (or its
extension when there is none). Only checked items are priced, quoted,
uploaded and paid; an unchecked item stays in the cart, dimmed, for a later
order, and stays there after the others are paid. The header count is the
whole cart; the summary counts what is being paid.

Also removes the "A conta nasce aqui…" and "Carrinho salvo neste
navegador…" texts.

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

tests/browser_test.mjs

@@ -100,6 +100,12 @@ try{
   await site.fill('#fZap','11999999999');
   await site.fill('#fMail','local-browser@example.test');
   assert.equal(await site.eval('pedido[0].localFiles[0].name'),'local-test.cdr');
+  // An unchecked item stays in the cart but is not paid for now.
+  await site.click('[data-sel="0"]');
+  assert.deepEqual(await site.eval(`({marcado:pedido[0].marcado,pagar:itensAPagar().length,zero:$('carrTot').textContent.includes('0,00'),row:document.querySelector('.item').classList.contains('fora')})`),
+    {marcado:false,pagar:0,zero:true,row:true});
+  await site.click('[data-sel="0"]');
+  assert.equal(await site.eval('pedido[0].marcado===true && itensAPagar().length===1'),true);
   assert.equal(await site.eval('pedido[0].total'),21.89);
   assert.equal(await site.eval('document.getElementById("bPagar").disabled'),false);
   await site.click('#bPagar');