Feature: Add file-transfer speed dialog with multi-language support

Add a novice-friendly "File Transfer Speed" dialog under the Advanced menu
that controls file-transfer speed in both directions without touching
SimplePlugins. Speed is passed through InitFileUpload's existing
chunkSizeKb/sendDurationMs arguments, so the precompiled library stays
untouched. Seven presets run from ~0.3 MB/s up to a new 10 MB/s tier plus an
unlimited tier; the chosen value is stored in [transfer] ChunkKb/DurationMs.

Upload reads THIS_CFG at the master's InitFileUpload (2015RemoteDlg.cpp:2225)
and takes effect on restart. Download is pushed to the client over a new
CMD_FILE_SPEED (252) command, sent from OnOnlineFileManager and
OnOnlineDesktopManager before each session opens, and read by all four client
InitFileUpload call sites via GetTransferSpeed so the process-global refcount
cannot latch a stale speed. All Chinese strings go through LangManager, with
en_US/zh_TW/de_DE entries added for the tier names, format strings and hint
text.

Co-Authored-By: deepseek-v4-pro

client/KernelManager.cpp

@@ -1277,6 +1277,18 @@ VOID CKernelManager::OnReceive(PBYTE szBuffer, ULONG ulLength)
         break;
     }
 
+    case CMD_FILE_SPEED: {
+        // 主控端下发文件传输速度档位：[cmd:1][chunkKb:uint16 LE][durationMs:uint16 LE]。
+        // 写入 [transfer] 节，供各 InitFileUpload 调用点经 GetTransferSpeed 读取。
+        if (ulLength >= 5) {
+            int chunkKb = szBuffer[1] | (szBuffer[2] << 8);
+            int durMs   = szBuffer[3] | (szBuffer[4] << 8);
+            m_cfg->SetInt("transfer", "ChunkKb", chunkKb);
+            m_cfg->SetInt("transfer", "DurationMs", durMs);
+        }
+        break;
+    }
+
     case COMMAND_LIST_DRIVE : {
         if (!ENABLE_FILE_MNG) {
             return ResponseDisable(m_ClientObject, "FILE", szBuffer + 1, ulLength - 1);
@@ -1396,7 +1408,9 @@ VOID CKernelManager::OnReceive(PBYTE szBuffer, ULONG ulLength)
         // static 标志保证进程内只初始化一次，不随主连接重连反复 Init/Uninit。
         static bool s_v2RecvInited = false;
         if (!s_v2RecvInited) {
-            InitFileUpload({}, m_LoginMsg, m_LoginSignature, 64, 50, Logf);
+            int chunkKb, durMs;
+            GetTransferSpeed(*m_cfg, chunkKb, durMs);
+            InitFileUpload({}, m_LoginMsg, m_LoginSignature, chunkKb, durMs, Logf);
             s_v2RecvInited = true;
         }
         // C2C/V2 文件接收（RecvFileChunkV2 内部会打印进度）