refactor: use nginx -s reload instead of systemd

- doc: add comment

internal/processlock/lock_linux_test.go

@@ -9,6 +9,8 @@ import (
 	"testing"
 )
 
+// TestLockUsesKernelOwnershipAndLeavesFileInPlace 验证锁由内核状态决定所有权、
+// 锁文件在释放后保留、写入诊断 PID，并可在释放后重新获取。
 func TestLockUsesKernelOwnershipAndLeavesFileInPlace(t *testing.T) {
 	t.Parallel()
 	path := filepath.Join(t.TempDir(), "serve.lock")