Add AGENTS.md for cloud development environment setup

[manucorporat]

Summary

Adds AGENTS.md with Cursor Cloud-specific development environment instructions for this Next.js 12 + Builder.io blog example.

What's included

• Node.js version requirement (Node 18 needed for Next.js 12 compatibility)
• Key development commands (dev server, lint, build)
• Architecture notes explaining the split between local MDX content and Builder.io CMS
• Known gotchas for cloud agent development

Environment verification

The development environment was fully set up and verified:

• Lint: npm run lint passes cleanly
• Dev server: npm run dev starts successfully on port 3000
• Build: npm run build completes without errors
• App functionality: Homepage renders blog posts, tags page works, navigation functional

Homepage showing blog posts
Tags page showing all blog tags

_{To show artifacts inline, enable in settings.}