dsh-task-todo: DeepSeek Harness To-Do Task Management Plugin

The `dsh-task-todo` plugin integrates task management into DeepSeek Harness. It supports multiple views (list, kanban, calendar, Gantt chart) and quick-add syntax, and provides a draggable floating-window mode. Agents can read and write tasks through `task_*` tools and the `/todo` command, with support for subtasks, recurring tasks, priorities, and checklist management. Data is globally synchronized and requires Node >= 22.