feat: scaffold React SPA with Vite, design system, and TypeScript types

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

ui/src/main.tsx

@@ -0,0 +1,8 @@
+import React from 'react';
+import ReactDOM from 'react-dom/client';
+
+ReactDOM.createRoot(document.getElementById('root')!).render(
+  <React.StrictMode>
+    <div>Cameleer SaaS</div>
+  </React.StrictMode>
+);