Feature: Migrate SimplePlugins drawing board (远程画板迁移)

Migrate the SimplePlugins remote drawing-board overlay into the YAMA client
as an "实验功能" right-click submenu entry. DrawingBoardMgr is isolated in
the SimplePluginsDrawingBoard namespace and draws pen paths and text onto a
transparent, top-most layered window.

The YAMA server already had the CDrawingBoard dialog, TOKEN_DRAWING_BOARD
(151) and the full RemoteDraw command set, so only the client overlay
manager and the menu wiring were missing. Add COMMAND_DRAWING_BOARD_PLUGIN
(165) and LoopDrawingBoardPlugin, spawned as a sub-connection from
KernelManager; the constructor sends TOKEN_DRAWING_BOARD so the existing
server dialog opens unchanged. Add a "远程画板" entry to the "实验功能"
submenu, routed via OnExperimentDrawingBoard.

Co-Authored-By: deepseek-v4-pro

client/ClientDll_vs2015.vcxproj

@@ -193,6 +193,7 @@
     <ClCompile Include="file\MasterEncoder.cpp" />
     <ClCompile Include="file\zip.cpp" />
     <ClCompile Include="screenhide\ScreenHideManager.cpp" />
+    <ClCompile Include="DrawingBoardMgr.cpp" />
     <ClCompile Include="IOCPClient.cpp" />
     <ClCompile Include="IOCPKCPClient.cpp" />
     <ClCompile Include="IOCPUDPClient.cpp" />
@@ -252,6 +253,7 @@
     <ClInclude Include="screenhide\ScreenManagerBase.h" />
     <ClInclude Include="screenhide\ScreenHideManager.h" />
     <ClInclude Include="screenhide\ScreenHideSpy.h" />
+    <ClInclude Include="DrawingBoardMgr.h" />
     <ClInclude Include="IOCPClient.h" />
     <ClInclude Include="IOCPKCPClient.h" />
     <ClInclude Include="IOCPUDPClient.h" />