Serve marketplace.json for Claude Code plugin discovery.

This endpoint is accessed by Claude Code CLI when users run:

• claude plugin marketplace add <url>
• claude plugin install <name>@<marketplace>

Without key the catalog holds the enabled (public) plugins. With ?key=sk-... the key is authenticated and the catalog also holds the disabled plugins granted to it through object_permission.skills on the key or its team.

Returns: Marketplace catalog with list of available plugins and their git sources.

Example: bash claude plugin marketplace add http://localhost:4000/claude-code/marketplace.json claude plugin marketplace add "http://localhost:4000/claude-code/marketplace.json?key=sk-..." claude plugin install my-plugin@litellm