Support local CLAUDE.md

Hello!

The rest of my team uses claude code (and thus the local CLAUDE.md file is committed in the repo). It would be great if opencode could directly read this so I don't have to create yet another file or add a config option in my config.

If opencode already supports this then maybe the docs just need to be updated? It would be nice if /init would detect and use this instead of creating a separate file as well.