Build Data Designer plugin catalog CLI core

[johnnygreco]

Summary

Implement the Data Designer core side of the plugin catalog and tap ecosystem described in the plugin ecosystem plan.

Scope

• Add a data-designer plugins CLI group for listing, searching, inspecting, installing, and listing installed plugins.
• Add tap configuration and catalog caching for the default NVIDIA tap and user-configured taps.
• Evaluate Python and Data Designer compatibility from static catalog metadata.
• Build installer plans for PyPI, git, local path, and URL sources, then verify runtime discovery through the existing PluginRegistry.
• Add tests for repository, service, install, and command behavior.

Notes

This work keeps plugin execution in the existing runtime registry and does not move plugin packages into core.