Add a sticky site footer

Adds a Footer with the brand, quick links (Menu, Basket, Your orders,
Help), and a copyright line, rendered on every page. Body is now a
full-height flex column so the footer sits at the bottom of the
viewport on short pages instead of floating right under the content.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/styles/globals.scss

@@ -46,6 +46,9 @@ html {
 
 body {
   margin: 0;
+  min-height: 100vh;
+  display: flex;
+  flex-direction: column;
   font-family:
     system-ui,
     -apple-system,