feat: implement header/footer visibility controls for checkout and thankyou pages

- Created LayoutWrapper component to conditionally render header/footer based on route
- Created MinimalHeader component (logo only)
- Created MinimalFooter component (trust badges + policy links)
- Created usePageVisibility hook to get visibility settings per page
- Wrapped ClassicLayout with LayoutWrapper for conditional rendering
- Header/footer visibility now controlled directly in React SPA
- Settings: show/minimal/hide for both header and footer
- Background color support for checkout and thankyou pages

admin-spa/src/routes/Appearance/index.tsx

@@ -0,0 +1,13 @@
+import React, { useEffect } from 'react';
+import { useNavigate } from 'react-router-dom';
+
+export default function AppearanceIndex() {
+  const navigate = useNavigate();
+  
+  useEffect(() => {
+    // Redirect to General as the default appearance page
+    navigate('/appearance/general', { replace: true });
+  }, [navigate]);
+  
+  return null;
+}