doc: Add remote control MCP design doc

Add docs/Mcp_RemoteControl_Design.md, the reference design for an
screenshot-driven AI remote-control feature: the existing get_screenshot for
observation plus remote_open/remote_close/remote_mouse/remote_keyboard for
input injection, reusing COMMAND_SCREEN_PREVIEW_REQ and COMMAND_SCREEN_CONTROL
+ MSG64. Coordinates are normalized (0..1) and mapped server-side to physical
pixels; injection runs over the screen sub-connection opened by
WebService::StartRemoteDesktop's hidden CScreenSpyDlg. Includes a
chat-on-behalf experiment case with clipboard-encoding and window-capture
notes.

Also fold in the get_audit_log encoding correction for
docs/Mcp_Terminal_Design.md, so the two doc changes ship as one commit.

Co-Authored-By: deepseek-v4-pro

docs/Mcp_Terminal_Design.md

@@ -451,7 +451,7 @@ McpServer().SetTerminalEnabled(THIS_CFG.GetInt("settings", "McpTerminal", 0) !=
 ### 10.6 中文/乱码
 
 - 输出乱码：检查 `isPty` 与 `cp` 是否匹配（PTY=UTF-8，老管道=GBK）。
-- **`get_audit_log` 中文乱码**：已知问题（GBK 写入 UTF-8 JSON），影响**所有**审计条目，非终端特有，暂未修复。
+- **`get_audit_log` 中文正确**：`BuildGetAuditLog` 用 `ToUtf8(type/time/msg, 936)` 把 GBK 转 UTF-8，jsoncpp 输出 `\uXXXX` 转义，客户端解析后中文正常（已实测 `MCP持久终端`/`MCP命令执行`/`操作成功`/`主机上线` 等均无乱码）。
 
 ### 10.7 会话泄漏 / 子链接不关