feat: Add internal agents app for repo automation (#11799)
Adds `apps/agents` for internal repo automation via Slack. Two
workflows:
1. **Security audit** — cron or manual trigger runs `cargo audit` +
`pnpm audit`. If vulns found, an Opus 4.6 agent in Vercel Sandbox fixes
them, uploads the diff to Blob, and posts to Slack for approval before
opening a PR.
2. **Issue triage** — AI classifies new issues for missing
reproductions, notifies Slack only when one is needed. You approve
before anything gets posted.
Both are human-in-the-loop. Setup in `.env.example`.
