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/WebService.h

@@ -104,6 +104,10 @@ public:
     // Resolution change notification
     void NotifyResolutionChange(uint64_t device_id, int width, int height, bool top_down = false, const std::string& client_type = "");
 
+    // 读回 NotifyResolutionChange 缓存的物理捕获分辨率（来自 TOKEN_BITMAPINFO）。
+    // 尚未收到分辨率时返回 false 并置 w/h 为 0。MCP 远程控制（remote_open）用它映射归一化坐标。
+    bool GetScreenSize(uint64_t device_id, int& width, int& height);
+
     // Audio enable/disable notification — pushes current state to all web
     // clients watching this device and caches it for newcomers.
     void NotifyAudioState(uint64_t device_id, bool enabled);