DeepSeek Harness Plugin: dsh-plugin-subagent-delete

DeepSeek Harness (DSH) lacks an interface for deleting subagents, causing their list to accumulate. The `dsh-plugin-subagent-delete` plugin fills this gap by providing tools and HTTP routes, including `list_subagents`, `delete_subagent` (for permanent deletion), and `release_subagent` (to release and restore subagents). It supports recursive operations, ownership validation, and automatic Web UI refresh, and is compatible with DSH 0.1.0-rc.8.