Add AgentShield — security scanner for AI agents

[elliotllliu]

AgentShield scans AI agent tools and plugins for backdoors, data exfiltration, and prompt injection before installation.

30 rules, AST taint tracking, cross-file analysis, 5-dimension scoring system. Zero install, 100% offline, MIT.

📦 https://www.npmjs.com/package/@elliotllliu/agent-shield