ci: fail PRs that carry AI attribution (#2224)

Adds a no-ai-attribution job to PR Build. It checks the PR title, the PR description and every PR commit message for AI co-author trailers and generated-with footers. CI result now depends on it, so a match blocks the merge. The workflow also re-runs when the PR title or description is edited.

Also corrects the header comment: CI result is a required check on main.

Author: CodeMazeBlog