Add AGENTS.md

[thedomeffm]

Would be super cool to see how the Symfony Team creates a AGENTS.md file for the demo project.

The ai-bundle already has the file => https://github.com/symfony/ai-bundle/blob/main/AGENTS.md

Sure I can create my own, but to see what you add to the coding rules would be super interesting.

[thedomeffm]

Perhaps @OskarStark or @chr-hertel could donate an AGENTS.md file for a standard Symfony application to the community? ❤️

[chr-hertel]

Hey @thedomeffm, i don't have a generic template at hand - maybe you could kick it off with /init (or similar) and then reference the best practice docs to be integrated?