[Feature Request] Clarify /clear command behavior with running background agents in documentation

**Bug Description**
claude:"The honest caveat: I don't know for certain whether /clear stops a running background agent mid-flight. If it does, the file never gets written. So either wait the few minutes, or clear and re-fire it — everything it reads is committed now, so the brief is fully reproducible from a cold session." ---> claude should probably be trained to know that

**Environment Info**
- Platform: linux
- Terminal: tmux
- Version: 2.1.269
- Feedback ID: 90bd81f8-0e81-4bfb-ac30-18252f64285f

**Errors**
```json
[]
```

Start by checking the existing /clear command documentation and its behavior while a background agent runs. Clarify whether /clear stops or preserves in-flight work, then document the observed result and any safe wait or re-fire guidance. Done means the behavior is stated unambiguously.

Written by the indexing model from the issue text.