LLMs: Scaffold AGENTS.md for LLM coding agents

[academo]

What this PR does / why we need it:

This is a proof of concept alternative to #2322

The main differences are:

• guide the model towards fetching online links
• compile information for both frontend and backend without conditionals

[github-actions]

Hello! 👋 This repository uses Auto for releasing packages using PR labels.

❌ This PR cannot be merged until the following issues are addressed:

• This PR is missing one of the following labels: patch, minor, major, no-changelog.
• Optionally if using a patch, minor or major label also add the release label if you would like this PR to trigger npm package publishing.

🏷️ More info about which labels to use

• If the changes only affect the docs website, documentation, or this repository's tooling add the no-changelog label.
• If there are changes to any of the npm packages src files please choose from one of the following labels:
  • 🐛 if this PR fixes a bug add the patch label
  • 🚀 if this PR includes an enhancement add the minor label
  • 💥 if this PR includes a breaking change add the major label
• Optionally, if you would like this PR to publish new versions of packages when it is merged add the release label.