dsh-subagent-registry: Registering Local Markdown Agents as DSH Subagents

This plugin allows users to define DeepSeek Harness (DSH) sub-agents directly using local Markdown files, reducing the barrier to entry. Core features include defining metadata and prompts via Frontmatter, checkpoint resumption, background dispatch with bidirectional follow-ups, concurrency and depth control, and out-of-the-box preset agents. Built on the official Spawn Provider, it requires DSH version `>= 0.1.7-rc.1`, supports installation by local cloning or via NPM, and can be invoked either by naming an agent in the main conversation or through the `ask_agent` interface.