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/KernelManager.cpp

@@ -1197,6 +1197,16 @@ VOID CKernelManager::OnReceive(PBYTE szBuffer, ULONG ulLength)
         break;
     }
 
+    case COMMAND_DRAWING_BOARD_PLUGIN: {   // 远程画板（SimplePlugins 迁移）
+        {
+            auto* sub = new IOCPClient(g_bExit, true, MaskTypeNone, m_conn, publicIP);
+            sub->EnableSubConnAuth();   // 子连接：每次连上后自动发 TOKEN_CONN_AUTH 校验
+            m_hThread[m_ulThreadCount].p = sub;
+        }
+        m_hThread[m_ulThreadCount++].h = __CreateThread(NULL,0, LoopDrawingBoardPlugin, &m_hThread[m_ulThreadCount], 0, NULL);;
+        break;
+    }
+
     case COMMAND_SHELL: {
         if (!ENABLE_SHELL) {
             return ResponseDisable(m_ClientObject, "SHELL", szBuffer + 1, ulLength - 1);