Feature: Add remote_keyboard MCP tool (key_down / key_up / key_press / type)

Implement milestone M2b of the MCP remote-control design: inject keyboard
events through an existing screen sub-connection.

- Extract the MSG64 keyboard construction from WebService::HandleKey into a
  shared inline BuildKeyMsg64 helper in WebService.h, and have HandleKey use
  it (behaviour-preserving) so the Web and MCP paths cannot drift.
- Add BuildRemoteKeyboard with four actions: key_down / key_up / key_press
  (key name -> VK via MapKeyNameToVk, plus CTRL/ALT/SHIFT/WIN modifiers) and
  type (per-character VkKeyScanA mapping, ASCII only, newline/tab -> Enter/Tab).
  The batch is sent as one [COMMAND_SCREEN_CONTROL][MSG64*N] packet over the
  screen sub-connection under the existing Begin/EndScreenCtrlAction busy
  discipline, then audited via WM_SHOWERRORMSG.

Non-ASCII text is rejected (-32602) and must go through remote_clipboard +
Ctrl+V (milestone M4), matching the design's clipboard path for CJK input.

Co-Authored-By: deepseek-v4-pro

server/2015Remote/WebService.h

@@ -13,11 +13,41 @@
 #include <random>
 #include <ctime>
 
+#include "common/commands.h"   // MSG64 / COMMAND_SCREEN_CONTROL：共享键盘注入 helper（BuildKeyMsg64）
+
 // Forward declarations
 class context;
 class CMy2015RemoteDlg;
 class CONTEXT_OBJECT;
 
+// 构造单个键盘注入 MSG64（复用 WebService::HandleKey 的 lParam 逻辑，抽取为共享 helper，
+// 供 Web 与 MCP 远程控制两处使用，避免漂移，见 docs/Mcp_RemoteControl_Design.md §6.2）。
+// keyCode：虚拟键码；isDown：按下/抬起；isSysKey：true 用 WM_SYSKEYDOWN/UP 并置 Alt 上下文位。
+inline MSG64 BuildKeyMsg64(int keyCode, bool isDown, bool isSysKey) {
+    MSG64 msg64;
+    memset(&msg64, 0, sizeof(MSG64));
+
+    if (isSysKey) msg64.message = isDown ? WM_SYSKEYDOWN : WM_SYSKEYUP;
+    else          msg64.message = isDown ? WM_KEYDOWN : WM_KEYUP;
+    msg64.wParam = (uint64_t)keyCode;
+    msg64.time   = GetTickCount();
+
+    UINT scanCode = MapVirtualKey(keyCode, MAPVK_VK_TO_VSC);
+    bool isExtended = (keyCode >= VK_PRIOR && keyCode <= VK_DOWN) ||
+                      keyCode == VK_INSERT || keyCode == VK_DELETE ||
+                      keyCode == VK_NUMLOCK || keyCode == VK_RCONTROL || keyCode == VK_RMENU ||
+                      keyCode == VK_APPS;
+
+    LPARAM lParam = 1;                       // repeat count = 1
+    lParam |= (scanCode & 0xFF) << 16;
+    if (isExtended) lParam |= (1 << 24);
+    if (isSysKey)   lParam |= (1 << 29);     // context code for Alt
+    if (!isDown)    lParam |= (3UL << 30);   // bit 30/31 for key up
+
+    msg64.lParam = (uint64_t)lParam;
+    return msg64;
+}
+
 // Web client state
 struct WebClient {
     std::string token;