Improve: three-state online host list sorting

Clicking the same column header now cycles ascending -> descending ->
restore default order instead of only toggling direction. The default order
is the host connection order, reconstructed by sorting on online time
(descending alive time) so it no longer depends on the in-memory append
order surviving an earlier sort. The reset preference is persisted as an
empty value so it survives a restart.

Co-Authored-By: deepseek-v4-pro

server/2015Remote/2015RemoteDlg.h

@@ -173,7 +173,7 @@ protected:
     DECLARE_MESSAGE_MAP()
 public:
     void SortByColumn(int nColumn);
-    void ApplySort();               // 按偏好重排 m_HostList（调用方需持有 m_cs）
+    void ApplySort();               // 按偏好重排 m_HostList；无偏好时恢复默认顺序（上线先后）（调用方需持有 m_cs）
     void LoadSortPreference();
     void SaveSortPreference();
     afx_msg VOID OnHdnItemclickList(NMHDR* pNMHDR, LRESULT* pResult);