dsh-powerdesk: Add a dockable IDE workspace to the DSH Web UI

dsh-powerdesk is a DSH web plugin maintained by FleetingEcho, designed to integrate terminals, file browsers, Markdown notes, code editors, sandboxed browsers, and calendars into dockable panels of the DSH Web UI to reduce app switching. The plugin requires DSH >= 0.0.1 and the dsh CLI to be in the PATH. Core features include a Rust-PTY based multi-instance terminal, a file manager supporting directory tree browsing and path copying, a notes module for recursive editing of local .md files, a CodeMirror 6-based multi-language syntax highlighting editor, a browser with secure sandbox mechanisms, and a calendar view with events stored in local SQLite. Additionally, the plugin supports ripgrep content search and panel fluidity.