fix-buildkite-ci

MEDIUM W011: Third-party content exposure detected (indirect prompt injection risk).

• Third-party content exposure detected (high risk: 1.00). SKILL.md and references/buildkite-ci-triage.md explicitly instruct the agent to fetch Buildkite build JSON, job logs, and artifacts via bk/curl from public Buildkite endpoints and then read/interpret those logs/artifacts to determine failures and apply fixes, which means the agent will ingest untrusted third-party (CI/log/artifact) content that can materially influence actions.