refactor: use nginx -s reload instead of systemd

- doc: add comment

internal/backendupdate/restart_test.go

@@ -11,6 +11,8 @@ import (
 	"yms-daemon/internal/transaction"
 )
 
+// TestRestartRejectsUnfinishedBackendUpdate 验证当存在未完成的后端更新事务时，Restart 会被拒绝，
+// 并返回 transaction.ErrActiveExists 及该活跃事务的记录。
 func TestRestartRejectsUnfinishedBackendUpdate(t *testing.T) {
 	ctx := context.Background()
 	store, err := transaction.OpenStore(ctx, filepath.Join(t.TempDir(), "transactions.db"))