Move desktop and e2e into examples/ directory

- desktop/ → examples/django-react-desktop-app/
- e2e/ → examples/django-react-site/
- example/ → examples/django-react-site/backend/
- Update Dockerfile.test, Makefile, playwright config, and
  django.config.mjs path references

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

examples/django-react-desktop-app/frontend/src/main.tsx

@@ -0,0 +1,4 @@
+import { createRoot } from 'react-dom/client'
+import { App } from './App'
+
+createRoot(document.getElementById('root')!).render(<App />)