Add AGENTS.md with Cursor Cloud development instructions

[manucorporat]

Summary

Adds AGENTS.md with Cursor Cloud specific development instructions for future cloud agents working on this codebase.

What's included

• Quick reference table for common dev commands (npm install, npm run dev, npm run lint, npm run build)
• Non-obvious notes about the project:
  • No automated test suite (validation via linting + manual testing)
  • Builder.io CMS dependency for blog post pages
  • No .env required for basic development
  • Husky pre-commit hooks run lint-staged
  • Build uses Preact swap

Demo

blog_demo_navigation_tags_theme.mp4

Dev environment fully working - homepage, tags, tag filtering, and theme toggle all functional.

Homepage in light mode
Homepage in dark mode

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