ci: add optional MCP Trust Kit scan

[aak204]

This adds a small optional GitHub Actions workflow example using MCP Trust Kit.

What changed:

• added .github/workflows/mcp-trust.yml
• added a short README note pointing to the workflow

Why this is useful:

• gives repos created from this template a copy-paste-friendly surface-risk check
• scans the local local-domain-checker.py entrypoint and uploads SARIF to GitHub code scanning
• stays workflow_dispatch-only by default, so it does not add a required CI gate

Project link:

• https://github.com/aak204/MCP-Trust-Kit