dsh-plugin-context-trim: DeepSeek Harness Session-Level Context Injection Gating

The DeepSeek Harness plugin `dsh-plugin-context-trim` addresses the context redundancy caused by indiscriminate injection of plugin capabilities across sessions. By leveraging a "shadow entry" mechanism, it allows users to trim Skills, Tools, MCP tools, and prompt sections on a per-session basis via the funnel button, with no residual artifacts and no cross-session impact. Features include batch management, state protection, hot activation, and default template saving, aiming to optimize context window utilization.