feat(client): add shadcn theme

- Added Nix theme
- Defaults to dark mode

Signed-off-by: Noa Virellia <noa@requiem.garden>

client/src/App.tsx

@@ -1,5 +1,11 @@
+import { ThemeProvider } from '@/components/theme-provider';
+
 function App() {
-  return <p>Hello world</p>;
+  return (
+    <ThemeProvider defaultTheme="dark" storageKey="vite-ui-theme">
+      <p>Hello world</p>
+    </ThemeProvider>
+  );
 }
 
 export { App };