Add premium configurator with split-screen layout

- Redesigned configurator page with split-screen interface
- Left: Large visual preview with sticky positioning
- Right: Premium white controls container with form steps
- Added complete configurator wizard (5 steps)
- Updated hero CTA to "Zelf ontwerpen"
- Configured Shadcn UI with Slate theme
- Added layout components (Navbar, Footer)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

components/layout/header.tsx

@@ -0,0 +1,11 @@
+import { TopBar } from "./top-bar";
+import { MainNav } from "./main-nav";
+
+export function Header() {
+  return (
+    <header className="sticky top-0 z-50 w-full shadow-sm">
+      <TopBar />
+      <MainNav />
+    </header>
+  );
+}