fix: configure CI database connection properly

- Add dotenv loading to Django settings
- Update CI workflow to use correct environment variables
- Set POSTGRES_* variables instead of DATABASE_URL
- Add environment variables to all Django management commands
- Fixes CI test failures due to database connection issues

app/requirements.txt

@@ -7,3 +7,5 @@ weasyprint==62.3
 python-dotenv==1.0.1
 requests==2.32.3
 gunicorn==22.0.0
+python-dateutil==2.9.0
+markdown==3.6