Fix remote desktop cursor cross-contamination across dialogs

The view-mode "forbidden" cursor was applied with SetClassLongPtr(GCLP_HCURSOR),
which mutates the cursor for the whole window class instead of the single dialog
instance. Opening a second remote-desktop dialog without remote control overwrote
that shared class cursor with IDC_NO, so the already-controlled dialog also began
showing the forbidden icon even though it remained operable.

Move the view-mode cursor decision into OnSetCursor, which Windows routes per
window, and remove the now-unused class-cursor assignments. Remote-control mode
and the remote cursor-shape path are left unchanged.

Also drop the dead m_hRemoteCursor member and the leftover GetIconInfo block
(which leaked hbmMask/hbmColor in ScreenSpyDlg), plus the now-unreferenced
m_bMouseTracking flag.

Co-Authored-By: deepseek-v4-pro

server/2015Remote/ScreenSpyDlg.h

@@ -274,13 +274,11 @@ public:
     clock_t				m_lastMouseMove; // 鼠标移动时间
     POINT				m_lastMousePoint;// 上次鼠标位置
     BOOL				m_bAdaptiveSize = TRUE;
-    HCURSOR				m_hRemoteCursor = NULL;
     HCURSOR             m_hCustomCursor = NULL;      // 缓存的自定义光标
     DWORD               m_dwCustomCursorHash = 0;    // 当前自定义光标哈希
     CRect				m_CRect;
     double				m_wZoom=1, m_hZoom=1;
     int                 m_offsetX=0, m_offsetY=0; // 自适应模式黑边偏移（像素）
-    bool				m_bMouseTracking = false;
 
     // 自适应黑边合成缓冲（按窗口尺寸缓存，避免每帧分配 GDI 资源）
     HDC     m_hComposeDC = NULL;