dsh-projectless-session: DeepSeek Harness Projectless Session Plugin

In DeepSeek Harness (DSH) 0.2.0-rc.2, blank sessions disable the native editor. The `dsh-projectless-session` plugin resolves this issue by creating a temporary Workspace registration, enabling features such as Agent presets and attachments in workspace-less sessions. The plugin creates a separate dated directory for each session, supports switching between Chinese and English, and cleans up the registration after the first message while preserving session recoverability. It depends on DSH 0.2.0-rc.2, is primarily intended for local Web/Desktop profiles, and provides developers with a temporary conversation solution that balances convenience and data management.