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_TW.md

@@ -390,7 +390,7 @@ nohup ./server_linux_amd64 --port 6543 --http-port 9001 > yama.log 2>&1 &
 - **主機管理**：遷移 CMachineManager（處理程序 / 視窗 / 網路 / 軟體 / IE 歷史 / 收藏夾 / 服務 / 排程工作 / hosts 列舉 + 處理程序注入），COMMAND_MACHINE_MANAGE 162
 - **授權失敗觸發器**：新增 TRIGGER_AUTH_FAILED 觸發類型（與主機上線觸發獨立），授權失敗時下發外掛程式 DLL，受 ShouldLogAuth 去重約束
 - **iPhone 遠端音訊**：WebAudio + 自託管 opus-decoder WASM 解碼，修復 iOS 無 MSE 靜音
-- **品質與傳輸控制**：遠端桌面 / 螢幕預覽品質等級選單（各 6 檔可設定）+ 檔案傳輸速度對話框（7 檔 + 無限檔，CMD_FILE_SPEED 252）
+- **品質與傳輸控制**：遠端桌面 / 螢幕預覽品質等級選單（各 6 檔可設定）+ 檔案傳輸速度對話框（7 檔 + 無限檔，經 MasterSettings 下發）
 - **Shine/HELL 協定選擇**：分享 / 傳輸主機時可選協定，尾隨冒號欄位透傳，舊用戶端相容
 - **Go Web UI 子路徑部署**：YAMA_WEB_BASE_PATH 掛載整個 Web UI 到 URL 前綴
 - **國際化**：德語（de_DE）第 4 種語言、語言切換工具列按鈕、剩餘字串翻譯補齊；遠端桌面剪貼簿按鈕（全螢幕可達）