security: sanitize internal infrastructure details from open source package

- Remove production_test_sequence.sh (DAW-specific production tests)
- Remove setup_env.sh (obsolete .env setup, replaced by furt.conf)
- Sanitize test scripts: replace dragons-at-work.de with example.com
- Sanitize API keys: replace dev keys with placeholder values
- Remove hardcoded DAW fallbacks from http_server.lua and smtp.lua
- Update .gitignore to exclude production-specific test files

Tests remain functional for developers with example domains.
All internal DAW infrastructure details removed from package.

Closes #101

.gitignore

@@ -68,3 +68,4 @@ config.production.lua
 
 config/furt.conf
 
+scripts/production_test_sequence.sh