feature request: ability to configure which file will contain agent rules #583

At my company we use a variety of llm tooling and we need to be able to have rule standards used across all of these tools, I feel like instead of extending the following in packages/opencode/src/session/system.ts:

  const CUSTOM_FILES = [
    "AGENTS.md",
    "CLAUDE.md",
    "CONTEXT.md", // deprecated
  ]

We could allow a user to override / extend this in their configuration potentially?

I realize during the /init we can do most of this but I don't wanna rerun that every time someone updates one of the rules (nor do I wanna copy it in haha)

If this is something that seems reasonable I am happy to open a PR.