dsh-cron-scheduler: A Linux crontab-Style Scheduled Task Scheduler Plugin

`dsh-cron-scheduler` is a DeepSeek Harness (DSH) plugin based on Linux cron syntax that allows LLMs to manage scheduled tasks directly in conversation. It supports 5/6-field cron expressions, steps, and ranges, with full lifecycle management including creation, listing, deletion, and proactive task suggestions. Tasks are bound to sessions for persistence and automatically restored after host restarts. Through semantic reasoning and confirmation mechanisms, the plugin converts LLM automation requirements into real scheduling, enabling periodic reminders and workflow invocations.