## Why
Standalone image generation needs a typed `codex-api` client surface for
the Codex image proxy routes before the harness and model-facing tool
layers are wired in.
## What changed
- Added `ImagesClient` support for JSON `images/generations` and
`images/edits` requests.
- Added typed request and response shapes for generation, JSON edit
image URLs, image metadata, and base64 image outputs.
- Kept generation model slugs open-ended while requiring the generation
model field that the downstream endpoint expects.
- Exported the new client and image types from `codex-api`.
- Added coverage for generation and edit wire shapes, extra response
metadata that the client ignores, and malformed image responses missing
`data`.
## Validation
- `cargo test -p codex-api`
- `just fix -p codex-api`
- `just fmt`
- `git diff --check main`
Won Park