feat: redesign the Site order flow and fix the cart layout

New landing (hero with a sheet preview, four steps, product cards priced
from the checkout table, price table and benefits), a progress bar that
follows the order through Montagem, Dados e entrega and Pagamento, the
live sheet beside the artworks, and a running total bar on phones.

The cart's saved-in-browser note no longer takes a grid column, which had
pushed the order into a narrow strip and the summary below it. The
previous look is kept in tag ui-v1.

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

web/cart.js

@@ -3,7 +3,7 @@
   let database,scope,timer,restoring=true;
   let signedOut=false;
   window.addEventListener('dtf-private-data-cleared',()=>{signedOut=true;clearTimeout(timer);pedido=[];itemAtual=null;folhas=[];artes=[];});
-  const notice=document.createElement('p');notice.style.cssText='font:13px system-ui;color:#56616d;padding:8px 20px';
+  const notice=document.createElement('p');notice.className='carrAviso';
   document.getElementById('carr').prepend(notice);
   function transaction(mode,fn){return new Promise((resolve,reject)=>{const tx=database.transaction('cart',mode);const request=fn(tx.objectStore('cart'));let result;request.onsuccess=()=>result=request.result;tx.oncomplete=()=>resolve(result);tx.onerror=()=>reject(tx.error);tx.onabort=()=>reject(tx.error);});}
   async function save(){