Add AGENTS.md for Cursor Cloud development environment setup

[computerbox124]

Summary

Adds AGENTS.md with Cursor Cloud-specific instructions for setting up and developing on the Huly Platform monorepo.

What's included

• Development environment prerequisites and key commands reference
• Docker service startup instructions (both minified and full stacks)
• Known gotchas (stale Rush lock files, validate timing, worker image not in min build)
• Links to existing docs for detailed architecture and setup

Environment setup verified

Check	Status
rush install	Pass
rush build	Pass (42s)
rush validate	Pass (71s)
rush format --to @hcengineering/core	Pass
rush test --to @hcengineering/core	Pass (981 tests)
Docker min stack (18 containers)	Running
Dev server (rushx dev-server)	Running at localhost:8080
Sign up + create workspace	Working end-to-end
Create tracker issue	Working end-to-end

Demo

huly_platform_demo_signup_and_create_issue.mp4

Issue TSK-1 "Hello World - Environment Setup Complete" created successfully, demonstrating full-stack operation.

Issue created in Huly tracker