fix: the footer stays at the bottom of the screen on short pages

On a short page (sign-in, an empty cart) the footer followed the content
and the rest of the screen was left blank below it, more so with the Site
drawn at 80%. The body is now a column at least the screen's height with
the footer pushed to its end; under the 80% zoom that height is 125vh,
because the zoom scales viewport units too.

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

web/site-shell.css

@@ -78,3 +78,7 @@ footer a:hover{color:var(--laranja2)}
 @media(max-width:720px){.fcont{margin-left:0;text-align:left}}
 .fbase{border-top:1px solid rgba(255,255,255,.1);padding-top:14px;display:flex;
  justify-content:space-between;gap:12px;flex-wrap:wrap;font-size:13.5px;color:#5A6570}
+
+/* The footer sits at the bottom of the screen even when the page is short. */
+body{display:flex;flex-direction:column;min-height:100vh}
+body>footer{margin-top:auto}

web/site-v2.css

@@ -488,5 +488,6 @@ html:is([data-rota="pagamento"],[data-rota="pix"]) .pagGrid{display:grid;grid-te
 
 /* On a computer the Site is drawn at 80%: the sizes above were chosen looking
    at it that way, and at 100% everything felt too big. Phones and tablets
-   keep their own sizes. */
-@media (min-width:1100px){html{zoom:.8}}
+   keep their own sizes. The zoom scales viewport units too, so the page's
+   full height is 125vh there (site-shell.css keeps the footer at the bottom). */
+@media (min-width:1100px){html{zoom:.8}body{min-height:125vh}}