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

scripts/start.sh

@@ -19,10 +19,10 @@ LUA_COMMAND=""
 # Config check first
 if [ "$(uname)" = "OpenBSD" ] || [ "$(uname)" = "FreeBSD" ]; then
     CONFIG_FILE="/usr/local/etc/furt/furt.conf"
-    PID_FILE="/var/run/furt.pid"
+    PID_FILE="/var/run/furt/furt.pid"
 else
     CONFIG_FILE="/etc/furt/furt.conf"
-    PID_FILE="/var/run/furt.pid"
+    PID_FILE="/var/run/furt/furt.pid"
 fi
 
 if [ ! -f "$CONFIG_FILE" ] && [ ! -f "$PROJECT_DIR/config/furt.conf" ]; then