fix(config): partial implementation of universal config detection (#68)

- Add multi-distribution config path detection
- Support /usr/local/etc/furt/environment (OpenBSD)
- Support /etc/furt/environment (Debian/Ubuntu/RHEL)
- Maintain .env support for development
- Add configurable Lua command via LUA_COMMAND environment variable

POSIX compatibility improvements:
- Replace command -v with [ -x ] for service user compatibility
- Change shebang from #!/bin/bash to #!/bin/sh for OpenBSD
- Replace ${BASH_SOURCE[0]} with $0 for POSIX shell compatibility

walter deployment changes:
- Migrate directory structure to /usr/local/furt/furt-lua/
- Set up _furt user permissions
- Configure system config in /usr/local/etc/furt/environment

Known issues:
- karl development environment regression (lua51 detection failed)
- walter SSL missing for SMTP (luasec vs luaossl compatibility)
- Config strategy needs comprehensive redesign for multi-implementation

Related: #68

Files modified:
- furt-lua/scripts/start.sh (POSIX compatibility + universal config)
- .env.example (added LUA_COMMAND and LUA_VERSION)
- walter: /usr/local/etc/furt/environment (system config setup)

.env.example

@@ -7,6 +7,10 @@ GITEA_TOKEN=your-gitea-token-here
 # Optional: Default-Assignee für Issues
 DEFAULT_ASSIGNEE=your-username
 
+# Lua-Konfiguration
+LUA_COMMAND=lua51
+LUA_VERSION=5.1
+
 # Gateway-Konfiguration (für Entwicklung)
 GATEWAY_PORT=8080
 GATEWAY_LOG_LEVEL=info