dsh-task-progress-notifier: Track todo_write task progress and trigger native desktop notifications

`dsh-task-progress-notifier` is a DeepSeek Harness (DSH) plugin designed to monitor changes in an agent's `todo_write` task status and notify users via native desktop notifications when a task starts, completes, or finishes all tasks. The plugin runs within the `dsh` profile and is licensed under the MIT license. Core features include tracking `todo/write` events and maintaining task snapshots to report only actual state transitions via differential comparison. It supports three notification modes: `notifyOnComplete` (single task completion), `notifyOnStart` (task start), and `notifyOnAllDone` (summary of all tasks completed), and provides `notify`.