Launch image generation by default

[won-openai]

Summary

• Promote image_generation from under-development to stable
• Enable image generation by default in the feature registry
• Update feature coverage for the new launch-state expectation
• Add the missing image-generation auth fixture field in a tool registry test

Testing

• just fmt
• cargo test -p codex-features
• cargo test -p codex-tools currently fails: test_full_toolset_specs_for_gpt5_codex_unified_exec_web_search needs its expected default tool list updated for image_generation

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 03c54c1bc4

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".