feat: ThemeProvider with light/dark toggle and localStorage persistence

src/main.tsx

@@ -1,13 +1,16 @@
 import { StrictMode } from 'react'
 import { createRoot } from 'react-dom/client'
 import { BrowserRouter } from 'react-router-dom'
+import { ThemeProvider } from './design-system/providers/ThemeProvider'
 import App from './App'
 import './index.css'
 
 createRoot(document.getElementById('root')!).render(
   <StrictMode>
     <BrowserRouter>
-      <App />
+      <ThemeProvider>
+        <App />
+      </ThemeProvider>
     </BrowserRouter>
   </StrictMode>,
 )