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>

Dockerfile.test

@@ -12,7 +12,7 @@ COPY django/ /app/django/
 RUN pip install --no-cache-dir /app/django[channels] daphne
 
 # Copy example app
-COPY example/ /app/example/
+COPY examples/django-react-site/backend/ /app/example/
 
 WORKDIR /app/example