Mark PR files as viewed

Take the trivial files off the reviewer's plate so they only read what matters. Marking a file as viewed is the only thing this skill writes to GitHub. Never approve, comment, or request changes.

1. Fetch

Use gh, not the browser. gh pr view --json files stops at 100 files, so page through the REST endpoint:

gh pr view <n> -R <owner/repo> --json id,title,headRefOid
gh api --paginate repos/<owner/repo>/pulls/<n>/files > files.json   # save to the scratchpad
jq -s 'add | length' files.json

Each entry has filename, previous_filename, status, additions, deletions and patch. Read the patches with jq -s -r 'add[] | select(...)', smallest first. Large files don't need their patches read, because they are never trivial.

2. Classify