@ottttto/dsh-scheduled-send: Server-Side Scheduled Send Plugin for DSH Web

`@ottttto/dsh-scheduled-send` is a scheduled messaging plugin that runs on the DeepSeek Harness (DSH) host side. It moves scheduling logic from the browser to the server, preventing task interruption when the browser is closed. The plugin supports adding a scheduling button to the input box, managing tasks in the sidebar, session isolation, resending after power failures, and mobile compatibility, making it suitable for scenarios such as simulating delayed conversations.