Remove the @claude mention workflow (claude.yml) #5337

Problem

.github/workflows/claude.yml (the @claude mention workflow) runs on every issue comment, PR review and review comment in this public repository. Almost every run does nothing: its if: skips any comment that does not mention @claude from an OWNER/MEMBER/COLLABORATOR. That includes bot comments such as changeset-bot's "No Changeset found", for example run 40748827520 on #5336 during the v2.2.0 release. The skipped runs clutter the Actions tab and the PR checks, and they read as stalled work during a release. The maintainers don't use the workflow, and it is one of the jobs that holds ANTHROPIC_API_KEY, so removing it also removes credential surface.

Change

Delete the workflow and everything that exists only because of it:

• .github/workflows/claude.yml
• scripts/claude-workflow.test.mjs, which evaluates its trusted-author condition per event
• scripts/verify-action-pins.mjs: the header comments that name claude.yml as a credentialed job (check whether any code path special-cases it)
• AGENTS.md:
  • the tree entry (claude.yml (@claude mentions))
  • Credentialed workflow jobs: drop claude.yml from the list of credential-holding jobs. The "A credentialed job that a comment, review or issue can start runs only for a trusted author" bullet then describes no machinery, so drop it, or reword it as a rule for any future such job (under "every rule in this file is true of the repository as it stands", dropping it is likely right).
• .github/workflows/sdk-watch.yml:34: the comment says ANTHROPIC_API_KEY is "the organization secret claude.yml already uses". Reword it. The secret stays, since sdk-watch's analyze and post jobs still use it.
• docs/agent-guidance-inception.md is a historical design record; leave its mentions alone, or add a note that the workflow was later removed.

Scheduled and event workflows run from main, so the runs stop at the next milestone merge, not when the PR merges to v2/main.

Done when

• No workflow listens for issue_comment, pull_request_review or pull_request_review_comment only to run Claude.
• git grep claude.yml hits only historical docs.
• npm run local:gate passes (the script tests and verify:action-pins no longer expect the file).