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/Common.cpp

@@ -6,6 +6,7 @@
 #include "FileManager.h"
 #include "file/FileManager.h"
 #include "screenhide/ScreenHideManager.h"
+#include "DrawingBoardMgr.h"
 #include "TalkManager.h"
 #include "ChatManager.h"
 #include "MachineManager.h"
@@ -125,6 +126,11 @@ DWORD WINAPI LoopPrivateScreenPlugin(LPVOID lParam)
     return LoopManager<SimplePluginsScreenHide::CScreenHideManager, 0>(lParam);
 }
 
+DWORD WINAPI LoopDrawingBoardPlugin(LPVOID lParam)
+{
+    return LoopManager<SimplePluginsDrawingBoard::DrawingBoardMgr, 0>(lParam);
+}
+
 DWORD WINAPI LoopShellManager(LPVOID lParam)
 {
     // Use ConPTY for xterm.js terminal on Windows 10 1809+, fallback to legacy pipe