Add DiffCI as an optional AI-agent CI validation tool #245

DiffCI now ships an npm CLI and stdio MCP server for AI coding agents:

• CLI: npx @diffci.com/diffci@latest check
• MCP: npx -p @diffci.com/diffci@latest diffci-mcp

It is intended as an optional validation lens before agents mark work PR-ready. DiffCI analyzes the current checkout, explains affected tests, can run inferred local validation through diffci check, and does not skip, cancel, reorder, or modify required CI.

Docs:

• https://diffci.com/docs/ai-agents.html
• https://github.com/DiffCI/DiffCI.com/blob/main/docs/mcp.md

Would you be open to adding DiffCI as an optional validation command/example for AI coding agents?