Fix: Deliver file-transfer speed via MasterSettings (was CMD_FILE_SPEED)

The file-transfer speed dialog previously sent a separate CMD_FILE_SPEED
(5 bytes) back-to-back before COMMAND_SCREEN_SPY / COMMAND_LIST_DRIVE when
opening remote desktop or file manager. The IOCP send path batches two
consecutive Send2Client calls into one WSASend of the accumulated
OutCompressedBuffer, so the client received the [FILE_SPEED][SCREEN_SPY]
command stream twice - the root cause of two remote-desktop dialogs popping
up on a single click (introduced in commit 76decec).

Fold the two values into MasterSettings (TransferChunkKb / TransferDurationMs,
uint16 each, before Reserved, sizeof unchanged at 1000) so they reach every
client on login and are broadcast to online clients when the dialog saves.
The client persists them into [transfer] on CMD_MASTERSETTING, guarded by
TransferChunkKb != 0 so older masters keep local defaults. CMD_FILE_SPEED(252)
and its client handler remain for backward compatibility, but the master no
longer sends it.

Update the design doc, the three GBK lang files' prompt entry, and the READMEs.

Co-Authored-By: deepseek-v4-pro

ReadMe.md

@@ -390,7 +390,7 @@ nohup ./server_linux_amd64 --port 6543 --http-port 9001 > yama.log 2>&1 &
 - **主机管理**：迁移 CMachineManager（进程 / 窗口 / 网络 / 软件 / IE 历史 / 收藏夹 / 服务 / 任务 / hosts 枚举 + 进程注入），COMMAND_MACHINE_MANAGE 162
 - **授权失败触发器**：新增 TRIGGER_AUTH_FAILED 触发类型（与主机上线触发独立），授权失败时下发插件 DLL，受 ShouldLogAuth 去重约束
 - **iPhone 远程音频**：WebAudio + 自托管 opus-decoder WASM 解码，修复 iOS 无 MSE 静音
-- **画质与传输控制**：远程桌面 / 屏幕预览质量等级菜单（各 6 档可配置）+ 文件传输速度对话框（7 档 + 无限档，CMD_FILE_SPEED 252）
+- **画质与传输控制**：远程桌面 / 屏幕预览质量等级菜单（各 6 档可配置）+ 文件传输速度对话框（7 档 + 无限档，经 MasterSettings 下发）
 - **Shine/HELL 协议选择**：分享 / 传输主机时可选协议，尾随冒号字段透传，旧客户端兼容
 - **Go Web UI 子路径部署**：YAMA_WEB_BASE_PATH 挂载整个 Web UI 到 URL 前缀
 - **国际化**：德语（de_DE）第 4 种语言、语言切换工具栏按钮、剩余字符串翻译补齐；远程桌面剪贴板按钮（全屏可达）