Support agents.md

Problem/Motivation

We are currently adding guidelines only to a handful of tools. That is because we are currently trying to write the guidelines from Surge to the tool specific mandatory directories
- Junie needs .junie/guidelines.md
- Claude needs Claude.md)

But it seems https://agents.md/ is gaining traction, and is supported already by quite a lot of agents, and others are following.

See for example JUNIE-618/Support-AGENTS.md.

Proposed resolution

I hope that ultimately that will become the default. Even if it's not at a full feature parity with things like .cursor/rules so lets make that our default, it seems like the best place to start.

Remaining tasks

- Change the standards/drupal-surge-standards.md to standards/AGENTS.md
- Update the Console Command so that people can choose the Agents.md as option
- Still support other formats (Claude / Junie)
- Help custom configurations
-- Configure Aider to use AGENTS.md in .aider.conf.yml
-- Configure Gemini CLI to use AGENTS.md in .gemini/settings.json
- Update documentation