DeepSeek Harness Plugin: dsh-plugin-cron

`dsh-plugin-cron-scheduler` is a scheduled task plugin for DeepSeek Harness (DSH), designed to automatically schedule Agent tasks using Cron expressions. It supports standard Cron syntax, session policies (new or fixed), and task creation via natural language instructions. The plugin provides a sidebar-based UI management interface and an HTTP API, supporting task persistence, concurrency protection, and execution history. Once installed, it enables automated workflow execution for Agents.