Add dd0c/route Dashboard UI: React + Vite + Tailwind SPA

- Layout with sidebar navigation (Dashboard, Rules, Keys, Settings)
- Dashboard page: stat cards, cost savings area chart (Recharts), model usage table
- Rules page: routing rules CRUD with modal editor, strategy/complexity/model matching
- Keys page: API key generation, copy-once reveal, revocation, quick-start code snippet
- Settings page: org info, provider config, danger zone
- API client (SWR + fetch wrapper) with full TypeScript types
- dd0c dark theme: indigo primary, cyan accent, dark surfaces
- Vite proxy config for local dev against API on :3000

products/01-llm-cost-router/ui/src/main.tsx

@@ -0,0 +1,13 @@
+import React from 'react';
+import ReactDOM from 'react-dom/client';
+import { BrowserRouter } from 'react-router-dom';
+import App from './App';
+import './index.css';
+
+ReactDOM.createRoot(document.getElementById('root')!).render(
+  <React.StrictMode>
+    <BrowserRouter>
+      <App />
+    </BrowserRouter>
+  </React.StrictMode>,
+);