dsh-agent-lead: DSH Team Lead Mode Plugin

`dsh-agent-lead` is a DSH plugin designed to address the problem of the main agent overfocusing on details and lacking control over model selection. By activating “Lead Mode,” it locks the main agent into a supervisor role responsible for planning, decomposition, task dispatch, and acceptance, while strictly prohibiting direct code changes. The plugin enforces task assignment through the `assign` tool and requires manual model selection for each task. It supports the `/lead` command for switching between manual and automatic modes, and uses a `scope` mechanism to prevent file conflicts. The main agent executes a lightweight work-order decision chain, intelligently routing tasks to existing subagents or newly created agents, and supports monitoring task queues, statuses, and re-reviews. It is suitable for scenarios that require strict collaboration and cost control.