fix: add protected-files policy to workshop-skill-activity-author

[Copilot]

workshop-skill-activity-author was failing to push because it lacked protected-files configuration — the safe-outputs infrastructure rejected the push when it encountered workshop/README.md under a request_review file-protection policy.

Changes

• .github/workflows/workshop-skill-activity-author.md — added protected-files.policy: request_review to the safe-outputs.create-pull-request block, matching the existing pattern in workshop-author.md:

safe-outputs:
  create-pull-request:
    ...
    protected-files:
      policy: request_review
    allowed-files:
      - "workshop/*.md"
      - "workshop/**/*.md"

• .github/workflows/workshop-skill-activity-author.lock.yml — recompiled lock file (gh aw compile --validate, 0 errors, 0 warnings)