Add AGENTS.md for Cursor Cloud development environment

[TravisDart]

Summary

Adds AGENTS.md with Cursor Cloud-specific instructions for developing and running the pull-index CLI in cloud agent environments.

What's documented

• How to run the CLI with uv
• Required external tools (AWS CLI, Docker)
• AWS credential requirements
• Docker setup notes for nested VM environments (fuse-overlayfs, socket permissions)
• Repository listing cache behavior
• Sanity-check commands (no formal test suite in repo)

Environment setup verified

• uv sync with Python 3.13.13
• uv run main.py --help
• list command cache resolution against s3://cold-qa01/2022-Q1/
• Docker daemon with Elasticsearch 8.11.0 image pull
• Python module compilation checks

VM update script: uv sync