feat(service): implement PID-file based service management

- Add PID directory creation in setup-directories.sh
- Update start.sh to use /var/run/furt/furt.pid for both platforms
- Fix OpenBSD rc.d script pidfile variable path
- Correct systemd service PIDFile parameter path
- Resolve rcctl check detection issues on OpenBSD

Fixes service detection problems where rcctl check would show (failed)
even when service was running. PID-file approach provides reliable
cross-platform service status detection instead of fragile pexp patterns.
Related DAW/furt#100

deployment/linux/furt.service

@@ -7,7 +7,7 @@ Type=forking
 User=furt
 Group=furt
 ExecStart=/usr/local/share/furt/scripts/start.sh
-PIDFile=/var/run/furt.pid
+PIDFile=/var/run/furt/furt.pid
 WorkingDirectory=/usr/local/share/furt
 Restart=always
 RestartSec=5