feat: add codex plugin setting

[zztnrudzz13]

Overview

Summary

• Add Codex plugin metadata for the React Design Philosophy plugin.
• Register the plugin in the local agents marketplace so it can be discovered and installed from this repository.
• Include plugin display metadata, prompts, capabilities, category, repository, homepage, and skill entrypoint configuration.

Test Plan

• Not run; configuration-only change.
• Verified the plugin metadata and marketplace registration files are present.

Checklist

• Did you write the test code?
• Have you run yarn run fix to format and lint the code and docs?
• Have you run yarn run test:coverage to make sure there is no uncovered line?
• Did you write the JSDoc?

[changeset-bot]

⚠️ No Changeset found

Latest commit: 43124a6

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[github-actions]

Size Change: 0 B 🆕

Total Size: 0 B

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[kimyouknow]

LGTM!