Add Codex integration and installer support

[zm2529]

What does this PR do?

Adds Codex integration support to The Agency.

This PR includes:

• convert.sh support for codex
• project-scoped Codex installer support in install.sh
• Codex documentation in README.md, integrations/README.md, and integrations/codex/README.md
• guidance for Chinese description support in Codex (description, vibe, and body may be localized, while name remains slug-friendly)
• .gitignore updates so generated Codex integration output stays local

Motivation

Issue #144 requested Codex support. This PR adds the missing conversion and installation flow, aligns the integration with the current tool list, and documents how to use it consistently with the other supported integrations.

Implementation Notes

• Codex skills are generated under integrations/codex/skills/<slug>/
• each skill includes:
  • SKILL.md
  • agents/openai.yaml
• installation is project-scoped and targets .codex/skills/
• generated integrations/codex/AGENTS.md is not committed
• Codex single-file output handling follows the current post-Fix convert.sh single-file output cross-contamination #186 gated output pattern
• tool lists and installer UI were updated to account for the current supported tools, including Qwen

Testing

Verified locally with:

• ./scripts/convert.sh --tool codex
• ./scripts/install.sh --tool codex
• ./scripts/convert.sh --tool all --parallel

Also confirmed:

• Codex installs into .codex/skills/
• generated integrations/codex/AGENTS.md stays local and is gitignored
• Chinese content in description fields is documented and supported without changing slug generation

Fixes #144.

Checklist

• Tested in real scenarios
• Proofread and formatted correctly

[msitarzewski]

Hey @zm2529 — thank you for working on this, and I'm sorry it sat so long without a proper response. That's on me.

It turns out four separate PRs came in for Codex integration (#160, #234, #293, #322) — the community clearly wants this! Rather than pick one in isolation, I'm closing all four and asking everyone to collaborate on a single approach in Discussion #206.

Please bring your work and ideas to that thread so we can land the best possible integration together.

Sorry for the delay: #206