dsh-workspace-upload: Moving workspace file management into the dsh chat interface

# Introduction When running agents using dsh's Web profile, the session workspace is where agents read and write files. However, the GUI itself lacks a file entry point: to hand a local CSV to the agent, one must first log in to the server and copy it into the workspace; to verify the artifacts just generated by the agent, one can only switch back to the terminal and run `ls`. dsh-workspace-upload fills this gap—allowing direct browsing, uploading, downloading, renaming, creating, and deleting files in the session workspace directly from the chat interface. The following sections introduce this plugin in the order of features, architecture, installation, and API. # What is it? dsh-workspace-upload (version 0.1.0, MIT License) is maintained by LI-Huaa and is