Protect spec-kit from AI slop PRs

> **Disclosure**: This issue was drafted with assistance from an AI coding agent (see your AGENTS.md / CONTRIBUTING.md for project policy on AI-assisted contributions). Submitted by a human (kimjune01) who reviewed the content.

7 of 89 PRs in the last 2 weeks would have been auto-closed before review.

Install a GitHub Action:

- [PR Quality Gate](https://github.com/kimjune01/sweep/blob/master/action.yml), judges PR quality not authorship, lets competent bots through, blocks lazy humans
- [anti-slop](https://github.com/peakoss/anti-slop), 34 configurable checks, built from maintaining Coolify (120 slop PRs/month)
- [agentscan-action](https://github.com/MatteoGabriele/agentscan-action), deep author profile analysis, detects automation patterns from account activity

[Full writeup](https://june.kim/speedrunning-open-source)