DeepSeek Harness Preset Agent Management Plugin

The `dsh-preset-agent-manager` plugin elevates preset agents to first-class citizens in DSH through a sidebar-based visual management panel. It enables the main agent to delegate tasks using the `preset_agent_dispatch` tool and ensures permission isolation and security in sub-sessions through independent plugin and tool allowlists. The plugin supports strict allowlist logic (inherited-layer masks and own-layer guards), delegation depth limits, and concurrency safety. It persists data to local JSON files and supports standard installation or manual configuration, effectively addressing the need to reuse and isolate permissions in multi-agent collaboration.