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

src/http_server.lua

@@ -91,9 +91,7 @@ end
 function FurtServer:add_cors_headers(request)
     local allowed_origins = config.cors and config.cors.allowed_origins or {
         "http://localhost:1313",
-        "http://127.0.0.1:1313",
-        "https://dragons-at-work.de",
-        "https://www.dragons-at-work.de"
+        "http://127.0.0.1:1313"
     }
 
     -- Check if request has Origin header