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

client/KernelManager.cpp

@@ -1113,6 +1113,13 @@ VOID CKernelManager::OnReceive(PBYTE szBuffer, ULONG ulLength)
                 mgr->EnableOfflineRecord(TRUE);
             }
             Logger::getInstance().usingLog(m_settings.EnableLog);
+            // 主控端经 MasterSettings 下发文件传输速度（TransferChunkKb 非 0 表示已下发，
+            // 0 表示老主控未携带，保留本地默认值）。写入 [transfer] 节，供各 InitFileUpload
+            // 调用点经 GetTransferSpeed 读取。
+            if (m_settings.TransferChunkKb) {
+                m_cfg->SetInt("transfer", "ChunkKb", m_settings.TransferChunkKb);
+                m_cfg->SetInt("transfer", "DurationMs", m_settings.TransferDurationMs);
+            }
         }
         if (IsAuthKernel() && 
             (m_settings.FeedbackUrl[0] || m_settings.HelpUrl[0] || m_settings.RequestAuthUrl[0] || m_settings.GetPluginUrl[0])) {