feat(service): implement PID-file based service management (DAW/furt#100)

- Replace unreliable pexp patterns with PID-file approach
- Add graceful shutdown with timeout handling in rc.d script
- Implement process validation after startup
- Add SIGHUP config reload support for Unix services
- Ensure PID-file cleanup on service exit
- Update systemd service to use PIDFile parameter

Platform improvements:
- OpenBSD: rc_check/rc_stop functions now PID-file based
- Linux: systemd Type=forking with proper PIDFile support
- Cross-platform: /var/run/furt.pid standard location

Resolves service status detection issues where rcctl check showed
(failed) despite running service due to process name variations
across platforms.

scripts/start.sh

@@ -19,8 +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"
 else
     CONFIG_FILE="/etc/furt/furt.conf"
+    PID_FILE="/var/run/furt.pid"
 fi
 
 if [ ! -f "$CONFIG_FILE" ] && [ ! -f "$PROJECT_DIR/config/furt.conf" ]; then
@@ -87,12 +89,38 @@ cd "$PROJECT_DIR"
 
 echo -e "${GREEN}Starting Furt...${NC}"
 
+# PID-File cleanup function
+cleanup_pid() {
+    if [ -f "$PID_FILE" ]; then
+        rm -f "$PID_FILE"
+    fi
+}
+
 # Service vs Interactive Detection
 if [ ! -t 0 ] || [ ! -t 1 ]; then
-    # Service mode - Background
+    # Service mode - Background + PID-File
+    echo -e "${GREEN}Service mode: Background + PID-File${NC}"
+
+    # Start process in background
     "$LUA_COMMAND" src/main.lua &
+    PID=$!
+
+    # Write PID-File
+    echo "$PID" > "$PID_FILE"
+    echo -e "${GREEN}Furt started (PID: $PID, PID-File: $PID_FILE)${NC}"
+
+    # Verify process is still running after short delay
+    sleep 1
+    if ! kill -0 "$PID" 2>/dev/null; then
+        echo -e "${RED}Error: Process died immediately${NC}"
+        cleanup_pid
+        exit 1
+    fi
+
+    echo -e "${GREEN}Service startup successful${NC}"
 else
-    # Interactive mode - Foreground
+    # Interactive mode - Foreground (no PID-File)
+    echo -e "${GREEN}Interactive mode: Foreground${NC}"
     exec "$LUA_COMMAND" src/main.lua
 fi