Add AGENTS.md with cloud-specific development instructions

[JavierCane]

Summary

Adds AGENTS.md with Cursor Cloud specific development instructions for this TypeScript library.

What's included

• Key commands table (install, lint, build, test)
• Notes on the missing test script in package.json and how to run Jest
• ESM compilation caveat (compiled dist/ requires tsx for direct execution)
• CI pipeline reference

Environment verification

All development tasks verified working:

• npm run lint — passes cleanly
• npm run build — compiles successfully
• npx jest — 1 test passes
• Hello world demo — McpClient instantiates correctly for both stdio and HTTP transports

dev_environment_output.log

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