Fix wrong data source for 404 analytics CSV download
- Update TrafficAnalyticsView.get() to check type=404 query param
- Add _get_csv_data_404() method for not-found pages CSV export
- Create project_traffic_analytics.html template with separate
download buttons for traffic and 404 analytics
- Add tests for both CSV download types
Co-authored-by: humitos <244656+humitos@users.noreply.github.com>
