## Summary
This updates the `js_repl` prompt and docs to make the image guidance
less confusing.
## What changed
- Clarified that `codex.emitImage(...)` adds one image per call and can
be called multiple times to emit multiple images.
- Reworded the image-encoding guidance to be general `js_repl` advice
instead of `ImageDetailOriginal`-specific behavior.
- Updated the guidance to recommend JPEG at about quality 85 when lossy
compression is acceptable, and PNG when transparency or lossless detail
matters.
- Mirrored the same wording in the public `js_repl` docs.