Fix environment variable handling for production deployment

- Update settings.py to support both ALLOWED_HOSTS and DJANGO_ALLOWED_HOSTS
- Add production CSRF_TRUSTED_ORIGINS for vhtv-stiftung.de
- Update env-template.txt with production variable examples
- Improve compatibility between development and production environments

.gitignore

@@ -111,3 +111,21 @@ celerybeat-schedule
 .mypy_cache/
 .dmypy.json
 dmypy.json
+
+logs
+dev-debug.log
+# Dependency directories
+# Environment variables
+# Editor directories and files
+.idea
+.vscode
+*.suo
+*.ntvs*
+*.njsproj
+*.sln
+*.sw?
+# OS specific
+
+# Task files
+# tasks.json
+# tasks/