Add Codex plugin marketplace metadata

[CoLaOnline]

Summary

• Add a single installable Codex plugin for Webflow with .codex-plugin/plugin.json, .agents/plugins/marketplace.json, and Codex MCP configuration.
• Expose all existing Webflow skills through a root skills/ directory so Codex can load them from one plugin.
• Keep the canonical skill source in the existing plugins/*/skills/* packs by using root-level symlinks instead of copying the skill files.
• Add scripts/codex-sync-from-packs.sh to regenerate the symlinked Codex skills/ view from the canonical plugin pack directories.

Why Codex packaging is different from Claude packaging

Claude uses .claude-plugin/marketplace.json to publish multiple plugin packs from this repo, with each marketplace entry pointing at a separate folder under plugins/. Each pack owns its own .claude-plugin/plugin.json and local ./skills/ directory.

For this PR, we want Codex to install one Webflow plugin. Codex expects a plugin root with .codex-plugin/plugin.json, and the manifest points to bundled components with plugin-relative paths such as "skills": "./skills/" and "mcpServers": "./.codex-mcp.json". Because the existing skills live across multiple plugin pack directories, the root skills/ directory acts as the single Codex-facing skill index while symlinking back to the canonical skill folders.

This keeps the Codex plugin install shape simple without introducing a second copied source of truth for the 24 Webflow skills.

Validation

• jq parses .agents/plugins/marketplace.json, .codex-plugin/plugin.json, .codex-mcp.json, and .mcp.json.
• scripts/codex-sync-from-packs.sh rebuilds 24 Codex-facing skill symlinks.
• find -L skills -maxdepth 2 -name SKILL.md resolves all 24 skills through the root skills/ directory.
• The Codex marketplace was registered successfully in a temporary Codex home.