Add a React Performance Goalkeeper for AI Programming with react-best-practices

### Official Vercel Agent Skill `react-best-practices` (formal name: `vercel-react-best-practices`) Introduction This skill organizes React/Next.js performance optimization experience into a rule set sorted by impact severity. The current `SKILL.md` contains 70 rules covering 8 categories, with priority given to eliminating request waterfalls and bundle bloat. Details include source attribution, the 8 rule categories, installation command (`npx skills add … --skill vercel-react-best-practices`), triggering usage in tools like Cursor, Claude Code and Codex, as well as applicable scenarios and notes on names and versions.