Prepare Expert System plugin 2.0.0 for Codex and Claude review

[spencer-g-smith]

Summary

• Add the repository-level Codex marketplace catalog so Expert System can be installed directly from GitHub.
• Present STARMODE (https://www.starmode.dev/) as the public plugin author, developer, and Claude marketplace owner.
• Update installation and release guidance, include the catalog in the package allowlist, and add identity/contract assertions.

Validation

• bun run typecheck, bun run lint, bun run format:check
• EXPERT_SYSTEM_SERVER_ROOT=../expert-system bun run plugin:check (7 passing tests)
• Strict Claude marketplace and plugin validation; bundled Codex plugin validation
• Fresh-clone candidate validation and a direct GitHub-branch Codex install (three skills, one MCP server) completed before the metadata-only branding change

Release gates

• Merge and deploy the companion server PR before directory submission.
• Claude first-login OAuth behavior and authentic v1-to-v2 upgrade remain unverified; see documents/plugin-release.md.
• No tag or plugin directory submission is part of this PR.

Companion server PR: starmode-base/expert-system#113