* feat(claude-code-plugin): add Claude Code plugin manifest
Adds .claude-plugin/plugin.json so the repo can be loaded as a Claude
Code plugin. Reuses the existing skills/ directory — all 5 skills
(hyperframes, gsap, hyperframes-cli, hyperframes-registry,
website-to-hyperframes) are auto-discovered under the hyperframes:
namespace.
* docs(readme): document Claude Code plugin usage
* chore(claude-code-plugin): add submission branding assets
* docs(claude-code-plugin): address review notes
