[vcauesantos]

Summary

• Add demo-command.yaml and demo-suite.yaml: a small, commented example of a PR comment command built on comment-triggered-check. Someone adding a command to another repo can copy both files.
• The command is /demo-e2e, so it does not clash with the /test-e2e harness here. A fake suite picks the result from the filter: ok passes, fail fails, nothing ends as "Nothing to run".
• Forks and the CI app are shown as commented-out lines.
• Add a README section.

Test plan

• actionlint passes. The local 1.7.12 only rejects the cache-mode key, which the existing harness uses too.
• zizmor reports only unpinned-uses on our own loft-sh/github-actions tags, which is expected.
• issue_comment only runs from main, so the live test runs after merge: /demo-e2e ok, fail, nothing and (ok on a test PR.