Add a smoothed bytes-per-second readout to the CDlgFileSend title,
refreshed about every 200 ms during transfer (e.g. "发送文件 - 5.3M/s").
The base title is captured on the first progress frame and the speed
suffix applied through Unicode APIs (GetWindowTextW / SetWindowTextW),
so the whole title stays correct on non-Chinese systems where the ANSI
message path would misdecode GBK as the system ACP.
Also add the missing "接收文件 (V2)" translation (en_US "Receive File (V2)",
zh_TW "接收檔案 (V2)"), so the V2 receive title no longer falls back to
raw Chinese on non-Chinese systems.
Co-Authored-By: deepseek-v4-pro
