DeepSeek Harness Plugin: dsh-session-reattach

`dsh-session-reattach` is a DSH host plugin designed to resolve misplaced "ungrouped" attribution for historical sessions caused by missing or moved directories. It only modifies the attribution records in `workspace.json`, leaving the session files themselves untouched, and operates in a safe dry-run mode by default. The plugin allows orphaned sessions to be restored to their proper `cwd` via the command line or by drag-and-drop in the sidebar, ensuring a tidy sidebar structure. After installation, restart `dsh web` to apply the changes.