Add AEO quality badge to README (score: 40/100)

Hi! I'm behind [Clarvia](https://clarvia.art) — an open quality scoring platform for AI/ML tools.

**Apache Airflow** has an AEO (Agent Experience Optimization) score of **40/100** on Clarvia.

Embed a live badge in your README:
```markdown
[![AEO Score](https://clarvia.art/api/badge/airflow)](https://clarvia.art/tool/airflow)
```

Full profile: https://clarvia.art/tool/airflow