Feature: Add persistent remote terminal MCP tools

Add terminal_open / terminal_exec / terminal_close so an AI can hold one
shell session per Windows host and run a sequence of commands with cwd and
environment preserved, instead of the one-shot exec_command.

The persistent terminal is a separate full-command write capability gated by
McpTerminal (default off) plus McpReadonly=0, with no whitelist and full
audit. One device maps to one terminal session via the shared m_TermSessions
map; idle sessions are swept after 300s. terminal_exec rejects commands that
contain & or | (they corrupt the sentinel control-operator chain) as well as
control characters.

Also harden exec_command and terminal_exec against newline/CR injection, fix a
dangling subCtx after an abrupt shell disconnect, and refresh lastActiveAt on
command completion. Add en/zh-TW translations for the new UI strings and a
design document covering both exec_command and the persistent terminal.

Co-Authored-By: deepseek-v4-pro

server/2015Remote/2015RemoteDlg.cpp

@@ -2193,6 +2193,8 @@ BOOL CMy2015RemoteDlg::OnInitDialog()
         // 安全配置：只读默认 1（exec_command 默认禁用）；白名单空则用内置只读前缀。
         McpServer().SetReadonly(THIS_CFG.GetInt("settings", "McpReadonly", 1) != 0);
         McpServer().SetCmdWhitelist(THIS_CFG.GetStr("settings", "McpCmdWhitelist", ""));
+        // 持久终端开关：默认关；要求只读关（McpReadonly=0）才生效（工具列表/分派双重门控）。
+        McpServer().SetTerminalEnabled(THIS_CFG.GetInt("settings", "McpTerminal", 0) != 0);
         if (!McpServer().Start(mcpBind, mcpPort)) {
             Mprintf("McpServer start failed on %s:%d\n", mcpBind.c_str(), mcpPort);
         } else {
@@ -5158,6 +5160,12 @@ BOOL CALLBACK CMy2015RemoteDlg::OfflineProc(CONTEXT_OBJECT* ContextObject)
         WebService().OnTerminalClosed(ContextObject);
     }
 
+    // MCP 终端（一次性 exec / 持久终端）的 shell 子上下文断开：同步清理会话，避免悬空 subCtx
+    // 被连接池复用时误路由新连接（与 WebService 清理同理，需在 RemoveFromHostList 之前）。
+    if (McpServer().IsRunning() && McpServer().IsTerminalContext(ContextObject)) {
+        McpServer().OnTerminalClosed(ContextObject);
+    }
+
     SOCKET nSocket = ContextObject->sClientSocket;
 
 	CDialogBase* p = (CDialogBase*)ContextObject->hDlg;