Implement the P2 upload_file tool to push a local file or directory from the
master to an online Windows host over the existing V2 file-transfer protocol.
The server drives FileBatchTransferWorkerV2 synchronously on the main
connection through a headless callback, reuses the list_files chain for the
overwrite pre-check, and is gated by McpFileTransfer=1 plus McpReadonly=0.
The client main connection never initialized the file-transfer module, so
g_status stayed 0 and RecvFileChunkV2 silently dropped every chunk, truncating
uploads to zero bytes. Add a once-per-process lazy InitFileUpload in the
COMMAND_SEND_FILE_V2 handler that mirrors the FileManager init; the destructor
deliberately does not Uninit so g_status remains 1 across reconnects.
Update the design doc to record the client-side change and correct the
upload_file description to state that sha256 is not returned (V2 has no
receiver-to-sender ACK; integrity is checked client-side and logged only).
Co-Authored-By: deepseek-v4-pro
6bcd593b6d