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

server/2015Remote/resource.h

@@ -1056,13 +1056,20 @@
 #define IDC_STATIC_SHARE_DAYS          2588
 #define IDC_EDIT_SHARE_DAYS            2589
 
+// 文件传输速度调节对话框
+#define IDD_FILE_SPEED                  403
+#define ID_TOOL_FILE_SPEED              33085
+#define IDC_FSPEED_SLIDER               2590
+#define IDC_FSPEED_LABEL                2591
+#define IDC_FSPEED_RESET                2592
+
 // Next default values for new objects
-// 
+//
 #ifdef APSTUDIO_INVOKED
 #ifndef APSTUDIO_READONLY_SYMBOLS
-#define _APS_NEXT_RESOURCE_VALUE        403
-#define _APS_NEXT_COMMAND_VALUE         33085
-#define _APS_NEXT_CONTROL_VALUE         2590
+#define _APS_NEXT_RESOURCE_VALUE        404
+#define _APS_NEXT_COMMAND_VALUE         33086
+#define _APS_NEXT_CONTROL_VALUE         2593
 #define _APS_NEXT_SYMED_VALUE           105
 #endif
 #endif