Suggestion: provide an AGENTS.md file for Solid v2 apps

[mathieuprog]

Inspired by Elixir/Phoenix, which now generates an AGENTS.md file when initializing a new app, it would be nice if Solid had something similar.

Ideally, this file would be maintained by the Solid team and cover Solid’s core mechanics, reactivity fundamentals, how Solid differs from React and other frameworks, idiomatic Solid v2 patterns, best practices, and common pitfalls.

This feels especially useful with Solid v2 coming, because agents may otherwise keep generating v1-style code, or code based on React assumptions. Solid is also still niche, with fewer training resources than larger frameworks, so official agent guidance could help produce better and more idiomatic Solid v2 code.