fix: 修复安装/升级无法重启服务的问题

backend/internal/pkg/sysutil/restart.go

@@ -0,0 +1,51 @@
+package sysutil
+
+import (
+	"fmt"
+	"log"
+	"os/exec"
+	"runtime"
+)
+
+const serviceName = "sub2api"
+
+// RestartService triggers a service restart via systemd.
+//
+// IMPORTANT: This function initiates the restart and returns immediately.
+// The actual restart happens asynchronously - the current process will be killed
+// by systemd and a new process will be started.
+//
+// We use Start() instead of Run() because:
+//   - systemctl restart will kill the current process first
+//   - Run() waits for completion, but the process dies before completion
+//   - Start() spawns the command independently, allowing systemd to handle the full cycle
+//
+// Prerequisites:
+//   - Linux OS with systemd
+//   - NOPASSWD sudo access configured (install.sh creates /etc/sudoers.d/sub2api)
+func RestartService() error {
+	if runtime.GOOS != "linux" {
+		return fmt.Errorf("systemd restart only available on Linux")
+	}
+
+	log.Println("Initiating service restart...")
+
+	// The sub2api user has NOPASSWD sudo access for systemctl commands
+	// (configured by install.sh in /etc/sudoers.d/sub2api).
+	cmd := exec.Command("sudo", "systemctl", "restart", serviceName)
+	if err := cmd.Start(); err != nil {
+		return fmt.Errorf("failed to initiate service restart: %w", err)
+	}
+
+	log.Println("Service restart initiated successfully")
+	return nil
+}
+
+// RestartServiceAsync is a fire-and-forget version of RestartService.
+// It logs errors instead of returning them, suitable for goroutine usage.
+func RestartServiceAsync() {
+	if err := RestartService(); err != nil {
+		log.Printf("Service restart failed: %v", err)
+		log.Println("Please restart the service manually: sudo systemctl restart sub2api")
+	}
+}