fix(storefront): polish footer

Add explicit :focus-visible outline to footer nav links so keyboard
users get a clear, on-brand focus indicator instead of relying on
inconsistent browser default outlines against the dark footer bg.

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

src/app/components/footer/footer.component.scss

@@ -54,6 +54,12 @@
     &:hover {
       color: #fff;
     }
+
+    &:focus-visible {
+      outline: 2px solid #fff;
+      outline-offset: 2px;
+      border-radius: 2px;
+    }
   }
 }