Feature: Add MCP remote_open/remote_close remote control sessions

Add M1 of MCP remote control (docs/Mcp_RemoteControl_Design.md): the
remote_open / remote_close tools plus the ScreenCtrlSession state machine.

remote_open establishes a hidden screen sub-connection by reusing
WebService::StartRemoteDesktop (COMMAND_SCREEN_SPY -> CScreenSpyDlg ->
RegisterScreenContext), polls for the sub-connection plus its physical
resolution (TOKEN_BITMAPINFO -> NotifyResolutionChange -> GetScreenSize),
then records the session (single device, single session, reverse-mapped
subCtx for OfflineProc cleanup) and returns {session_id, screen_w,
screen_h}. remote_close validates session_id and tears down the
sub-connection idempotently. A McpRemoteControl settings checkbox (default
off, requires McpReadonly=0) gates the tools; every open/close is audited
via WM_SHOWERRORMSG.

Gating: multi-monitor hosts are rejected with -32008 (phase 1 supports only
single monitor, where Observe=main screen and Act=virtual desktop coincide);
the monitor count comes from the client heartbeat RES_RESOLUTION ("N:W*H").

Known limitations (deferred to the injection milestones): mutual exclusion
with human remote-desktop viewing is one-directional in M1 (a human who
joins during an MCP session can tear it down on disconnect), and subCtx is
not yet dereferenced so no liveness re-check is needed until
remote_mouse/remote_keyboard.

Co-Authored-By: deepseek-v4-pro

server/2015Remote/McpSettingsDlg.h

@@ -29,6 +29,7 @@ private:
         IDC_MCP_READONLY  = 1005,  // 「只读模式」复选框（默认勾选，禁 exec_command）
         IDC_MCP_WHITELIST = 1006,  // 命令白名单编辑框（多行，逗号/换行分隔，空 = 内置只读前缀）
         IDC_MCP_TERMINAL  = 1007,  // 「启用持久终端」复选框（全命令，无白名单，要求只读关）
+        IDC_MCP_REMOTECONTROL = 1008,  // 「启用远程控制」复选框（AI 操控桌面，要求只读关）
     };
 
     CButton m_btnEnable;
@@ -36,6 +37,7 @@ private:
     CEdit   m_editPort, m_editBind, m_editToken;
     CButton m_btnReadonly;
     CButton m_btnTerminal;
+    CButton m_btnRemoteControl;
     CStatic m_lblWhitelist;
     CEdit   m_editWhitelist;
     CButton m_btnOK, m_btnCancel;