dsh-agy-safe: Local Antigravity CLI Headless Session Integration Layer

The DeepSeek Harness plugin `dsh-agy-safe` addresses the pain points of remote API key management by integrating an already authenticated local Antigravity CLI (`agy`) session into DeepSeek Harness as a first-class model provider. It supports both main conversation and subagent calls, with features including headless session bridging, tool call adaptation, and accurate TPS metering. Developers need to install and configure it in a Node.js 20+ environment, complete login verification in the terminal, and then use the `agy` model in the Web interface. The plugin reuses the local official session, with credentials and usage remaining under the user's own account.