codex image and VQA provider

codex means Codex supplies image generation or image inspection even when the main project runner is not Codex.

Project config

asset_image_model: codex
vqa_model: codex

Setup

1. Install Codex and sign in.
2. Make sure the codex command is on PATH.
3. Run python tools/check_env.py.

This provider does not require an image API key. It does require the active Codex environment to expose the needed image or vision capability.