Add agent-safety-preflight plugin

[el-zachariah]

Adds a free agent-safety-preflight Claude Code plugin command under Security, Compliance, & Legal.

Why it fits this list:

• Claude Code slash command packaged with .claude-plugin/plugin.json.
• Helps users run a local repo preflight before tool-enabled Claude Code sessions get shell/package/MCP/secret-adjacent scope.
• Links only to the free public scanner/source repo for inspection; no checkout or paid-product link in this listing.

Validation performed:

• plugin.json parsed successfully.
• README entry and command markers verified locally.
• Duplicate code search for agent-preflight, agent-safety-preflight, and ai-agent-safety-starter-pack returned no upstream hits before submission.